NotifyHub — Unified Notification MCP Server

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Stop writing different code for each notification channel. NotifyHub gives you a single fluent API to send notifications via Email, SMS, WhatsApp, Slack, Telegram, Discord, Microsoft Teams, Firebase Push, Webhooks, WebSocket, Google Chat, Twitter/X, LinkedIn, Notion, Twitch, YouTube, Instagram, SendGrid, TikTok Shop, Facebook, AWS SNS, Mailgun, PagerDuty, Kick — or any custom channel you create.

notify.to(user)
    .via(EMAIL)
    .fallback(SMS)
    .priority(Priority.HIGH)
    .subject("Order confirmed")
    .template("order-confirmed")
    .param("orderId", order.getId())
    .attach(invoicePdf)
    .send();

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Why NotifyHub?

	Problem	Without NotifyHub	With NotifyHub
	Email	JavaMail config, MIME types, Session...	.via(EMAIL)
📱	SMS	Twilio SDK, different API entirely	.via(SMS)
	WhatsApp	Another Twilio setup, prefix logic	.via(WHATSAPP)
	Slack	Webhook HTTP, JSON payload	.via(SLACK)
	Telegram	Bot API, HTTP client setup	.via(TELEGRAM)
	Discord	Webhook HTTP, JSON payload	.via(DISCORD)
👥	Teams	Incoming Webhook, MessageCard JSON	.via(TEAMS)
	Push	Firebase Admin SDK, credentials...	.via(PUSH)
🔗	Webhook	Custom HTTP, payload template	.via(Channel.custom("pagerduty"))
	WebSocket	Java WebSocket API, reconnect logic	.via(WEBSOCKET)
	Google Chat	Webhook HTTP, JSON payload	.via(GOOGLE_CHAT)
	Twitter/X	OAuth 1.0a, API v2 setup	.via(TWITTER)
💼	LinkedIn	OAuth 2.0, REST API setup	.via(LINKEDIN)
	Notion	Integration Token, API setup	.via(NOTION)
	Twitch	OAuth 2.0, Twitch API setup	.via(TWITCH)
	YouTube	YouTube Data API v3 setup	.via(YOUTUBE)
	Instagram	Meta Graph API setup	.via(INSTAGRAM)
📧	SendGrid	SendGrid API, webhook tracking	.via(Channel.custom("sendgrid"))
	TikTok Shop	HMAC-SHA256, Shop API	.via(TIKTOK_SHOP)
	Facebook	Graph API, Page tokens	.via(FACEBOOK)
☁️	AWS SNS	AWS SDK, credentials, ARN	.via(Channel.custom("aws-sns"))
	Mailgun	Mailgun API, domain setup	.via(Channel.custom("mailgun"))
	PagerDuty	Events API v2, routing key	.via(Channel.custom("pagerduty"))
	Kick	Public API, OAuth 2.1	.via(KICK)
	Multiple channels	Completely different code for each	Same fluent API
Fallback	Manual try/catch chain	.fallback(SMS)
Retry	Implement yourself	Built-in exponential backoff
Async	Thread pools, CompletableFuture	.sendAsync()
Scheduling	ScheduledExecutor, timer logic	.schedule(Duration.ofMinutes(30))
Templates	Each channel has its own engine	One template, all channels
i18n	Manual locale resolution	.locale(Locale.PT_BR)
Rate limiting	Token bucket from scratch	Config-driven per-channel
Tracking	Build your own delivery log	Built-in receipts + JPA
Dead letters	Lost in the void	Auto-captured in DLQ
Deduplication	Track sent messages yourself	Built-in content hash / explicit key
Template versions	Manage files manually	.templateVersion("v2") + A/B test
Batch	Loop and pray	.toAll(users).send()
Monitoring	Wire Micrometer yourself	Auto-configured counters
Health checks	Write an Actuator indicator	Auto-configured
Admin UI	Build your own dashboard	Built-in /notify-admin
Circuit breaker	Implement yourself per channel	Built-in per-channel circuit breaker
Orchestration	Manual escalation logic	.orchestrate().first(EMAIL).ifNoOpen(24h).then(PUSH)
A/B testing	External service + glue code	Built-in .abTest("exp").variant(...).split(50,50)
Testing	Mock everything	TestNotifyHub captures all sends
New channel	Build from scratch	Implement one interface

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Table of Contents

• Quick Start
• Features
  • Fallback Chain
  • Multi-Channel Send
  • Async Sending
  • Retry with Backoff
  • Templates (Mustache)
  • i18n (Internationalization)
  • Attachments
  • Priority Levels
  • Rate Limiting
  • Dead Letter Queue (DLQ)
  • Batch Send
  • Delivery Tracking
  • Scheduled Notifications
  • Notification Routing
  • Notifiable Interface
  • Message Deduplication
  • Template Versioning
  • Custom Channels
  • Event Listeners + Spring Events
  • Named Recipients
  • Message Queue (RabbitMQ / Kafka)
  • Circuit Breaker
  • Bulkhead (Concurrency Isolation)
  • Multi-Channel Orchestration
  • A/B Testing
  • Cron Scheduling
  • Quiet Hours
  • Testing Utilities
• Supported Channels
• Admin Dashboard
• Spring Boot Integration
• Configuration Reference
• Without Spring Boot
• MCP Server (AI Agents)
• Running the Demo
• Architecture
• Maven Central
• Roadmap
• License

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Quick Start

1. Add the dependency

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-spring-boot-starter</artifactId>
    <version>1.0.0</version>
</dependency>

Need extra channels? Add optional modules:

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-sms</artifactId>
    <version>1.0.0</version>
</dependency>


<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-slack</artifactId>
    <version>1.0.0</version>
</dependency>


<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-websocket</artifactId>
    <version>1.0.0</version>
</dependency>

2. Configure in application.yml

notify:
  channels:
    email:
      host: smtp.gmail.com
      port: 587
      username: ${GMAIL_USER}
      password: ${GMAIL_PASS}
      from: noreply@myapp.com
      from-name: MyApp
      tls: true
  retry:
    max-attempts: 3
    strategy: exponential
  tracking:
    enabled: true

3. Inject and use

@Service
public class OrderService {

    private final NotifyHub notify;

    public OrderService(NotifyHub notify) {
        this.notify = notify;
    }

    public void confirmOrder(Order order) {
        notify.to(order.getCustomer())
            .via(Channel.EMAIL)
            .subject("Order confirmed!")
            .template("order-confirmed")
            .param("customerName", order.getCustomer().getName())
            .param("orderId", order.getId())
            .param("total", order.getTotal())
            .send();
    }
}

That's it. Three steps.

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Features

Fallback Chain

If the primary channel fails, automatically try the next one:

notify.to(user)
    .via(Channel.WHATSAPP)
    .fallback(Channel.SMS)
    .fallback(Channel.EMAIL)
    .template("payment-reminder")
    .param("amount", "R$ 150,00")
    .send();
// Tries WhatsApp -> SMS -> Email

Multi-Channel Send

Send through ALL channels simultaneously:

notify.to(user)
    .via(Channel.EMAIL)
    .via(Channel.SLACK)
    .via(Channel.TEAMS)
    .subject("Security Alert")
    .content("Login from a new device detected")
    .sendAll();

Async Sending

Send notifications without blocking:

// Fire and forget
notify.to(user)
    .via(Channel.EMAIL)
    .template("welcome")
    .sendAsync();

// Or wait for result
CompletableFuture<Void> future = notify.to(user)
    .via(Channel.EMAIL)
    .via(Channel.SLACK)
    .content("Deploy complete!")
    .sendAllAsync();

future.thenRun(() -> log.info("All notifications sent!"));

Retry with Backoff

Automatic retry with exponential or fixed backoff:

# application.yml (global)
notify:
  retry:
    max-attempts: 3
    strategy: exponential  # waits 1s, 2s, 4s...

// Or per-notification
notify.to(user)
    .via(Channel.EMAIL)
    .retry(3)
    .template("invoice")
    .send();

Templates (Mustache)

Create templates in src/main/resources/templates/notify/:

order-confirmed.html (auto-used for email):

<h1>Hello, {{customerName}}!</h1>
<p>Your order <strong>#{{orderId}}</strong> has been confirmed.</p>
<p>Total: <strong>{{total}}</strong></p>

order-confirmed.txt (auto-used for SMS/WhatsApp/Slack/Telegram/Discord/Teams):

Hello {{customerName}}, your order #{{orderId}} is confirmed. Total: {{total}}

The library picks .html for email and .txt for other channels automatically.

i18n (Internationalization)

Templates support locale-based resolution with automatic fallback:

// User with locale
notify.to(user)
    .via(Channel.EMAIL)
    .locale(Locale.forLanguageTag("pt-BR"))
    .template("welcome")
    .param("name", user.getName())
    .send();

Template resolution order: welcome_pt_BR.html -> welcome_pt.html -> welcome.html

Your Notifiable can also return a locale:

public class User implements Notifiable {
    @Override
    public Locale getLocale() {
        return Locale.forLanguageTag("pt-BR");
    }
}

Attachments

Attach files to email notifications:

notify.to(user)
    .via(Channel.EMAIL)
    .subject("Your Invoice")
    .template("invoice")
    .attach("invoice.pdf", pdfBytes, "application/pdf")
    .attach(new File("/reports/monthly.xlsx"))
    .attach(Attachment.fromFile(contractFile))
    .send();

Priority Levels

Set notification priority. URGENT notifications bypass rate limiting:

notify.to(user)
    .via(Channel.EMAIL)
    .priority(Priority.URGENT)
    .subject("SERVER DOWN!")
    .content("Production server is unresponsive")
    .send();

Available priorities: URGENT (bypasses rate limits), HIGH, NORMAL (default), LOW.

Rate Limiting

Control notification throughput per-channel:

notify:
  rate-limit:
    enabled: true
    max-requests: 100
    window: 1m
    channels:
      email:
        max-requests: 50
        window: 1m
      sms:
        max-requests: 10
        window: 1m

Rate limiting uses a token bucket algorithm. URGENT priority notifications always bypass rate limits.

Dead Letter Queue (DLQ)

Failed notifications (after all retries) are automatically captured in the DLQ:

notify:
  tracking:
    enabled: true
    dlq-enabled: true

View and manage dead letters via the admin dashboard at /notify-admin/dlq, or programmatically:

DeadLetterQueue dlq = hub.getDeadLetterQueue();
List<DeadLetter> failed = dlq.findAll();
dlq.remove(deadLetterId); // after manual reprocessing

Batch Send

Send notifications to multiple recipients at once:

// By email addresses
notify.toAll(List.of("user1@test.com", "user2@test.com", "user3@test.com"))
    .via(Channel.EMAIL)
    .subject("System Maintenance")
    .template("maintenance-notice")
    .param("date", "2025-03-01")
    .send();

// By Notifiable entities
notify.toAllNotifiable(users)
    .via(Channel.EMAIL)
    .template("newsletter")
    .send();

// Async batch
notify.toAll(recipients)
    .via(Channel.EMAIL)
    .template("promo")
    .sendAsync();

Delivery Tracking

Track every notification with delivery receipts:

notify:
  tracking:
    enabled: true
    type: memory  # or "jpa" for database persistence

// Send and get a receipt
DeliveryReceipt receipt = notify.to(user)
    .via(Channel.EMAIL)
    .content("Hello!")
    .sendTracked();

System.out.println(receipt.getStatus());    // SENT
System.out.println(receipt.getId());         // uuid
System.out.println(receipt.getTimestamp());  // 2025-01-15T10:30:00Z

For database persistence, add the JPA tracker module:

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-tracker-jpa</artifactId>
    <version>1.0.0</version>
</dependency>

notify:
  tracking:
    enabled: true
    type: jpa

Scheduled Notifications

Schedule notifications for future delivery:

ScheduledNotification scheduled = notify.to(user)
    .via(Channel.EMAIL)
    .subject("Reminder")
    .content("Don't forget your appointment tomorrow!")
    .schedule(Duration.ofHours(24));

// Check status
scheduled.getStatus();        // SCHEDULED, SENT, FAILED, CANCELLED
scheduled.getRemainingDelay(); // PT23H59M...

// Cancel if needed
scheduled.cancel();

Notification Routing

Auto-route notifications based on user preferences:

public class User implements Notifiable {
    @Override
    public List<Channel> getPreferredChannels() {
        return List.of(Channel.WHATSAPP, Channel.SMS, Channel.EMAIL);
    }
}

// Auto-routes: WhatsApp (primary) -> SMS (fallback) -> Email (fallback)
notify.notify(user)
    .template("order-update")
    .param("orderId", "12345")
    .send();

Conditional routing with rules:

NotificationRouter router = NotificationRouter.builder()
    .rule(RoutingRule.timeBasedRule(
        LocalTime.of(9, 0), LocalTime.of(18, 0),
        Channel.SLACK, Channel.EMAIL))  // Slack during business hours, email after
    .build();

Notifiable Interface

Make your User entity a notification recipient:

@Entity
public class User implements Notifiable {

    private String name;
    private String email;
    private String phone;

    @Override
    public String getNotifyEmail() { return email; }

    @Override
    public String getNotifyPhone() { return phone; }

    @Override
    public String getNotifyName() { return name; }

    @Override
    public Locale getLocale() { return Locale.forLanguageTag("pt-BR"); }

    @Override
    public List<Channel> getPreferredChannels() {
        return List.of(Channel.EMAIL, Channel.SMS);
    }
}

Then just pass the user object:

notify.to(user)       // resolves email/phone automatically
    .via(Channel.EMAIL)
    .template("welcome")
    .send();

Or use raw addresses:

notify.to("user@email.com").via(Channel.EMAIL).content("Hello!").send();
notify.toPhone("+5511999999999").via(Channel.SMS).content("Code: 1234").send();

Message Deduplication

Prevent duplicate notifications automatically with content hashing or explicit keys:

notify:
  deduplication:
    enabled: true
    ttl: 24h
    strategy: content-hash  # content-hash | explicit-key | both

// Auto-dedup by content hash (same recipient + channel + content = skipped)
notify.to(user).via(EMAIL).content("Order confirmed").send();
notify.to(user).via(EMAIL).content("Order confirmed").send(); // skipped!

// Dedup by explicit key
notify.to(user).via(EMAIL)
    .deduplicationKey("order-" + orderId)
    .template("order-confirmed")
    .send();

Strategies:

• content-hash — SHA-256 hash of recipient + channel + subject + content
• explicit-key — uses the key provided via .deduplicationKey("...")
• both — uses explicit key if provided, otherwise falls back to content hash

Without Spring Boot:

NotifyHub notify = NotifyHub.builder()
    .deduplicationStore(new InMemoryDeduplicationStore(Duration.ofHours(12)))
    .channel(emailChannel)
    .build();

Template Versioning

Manage multiple versions of templates for A/B testing or gradual rollouts:

templates/notify/
├── order-confirmed.html           ← default version
├── order-confirmed@v1.html        ← version v1
├── order-confirmed@v2.html        ← version v2
├── order-confirmed_pt_BR@v2.html  ← v2 with i18n
└── order-confirmed.txt            ← text default

// Use a specific version
notify.to(user).via(EMAIL)
    .template("order-confirmed")
    .templateVersion("v2")
    .param("orderId", "123")
    .send();

// No version = default template (backward compatible)
notify.to(user).via(EMAIL)
    .template("order-confirmed")
    .send();

// A/B testing
String version = abTestService.getVariant(user, "email-template");
notify.to(user).via(EMAIL)
    .template("welcome")
    .templateVersion(version)  // "v1" or "v2"
    .send();

Resolution order: {name}@{version}_{locale}.{variant} → {name}@{version}.{variant} → {name}_{locale}.{variant} → {name}.{variant}

Custom Channels

Create your own channel by implementing one interface:

@Component
public class PushChannel implements NotificationChannel {

    @Override
    public String getName() { return "push"; }

    @Override
    public void send(Notification notification) {
        firebaseClient.send(notification.getRecipient(), notification.getRenderedContent());
    }

    @Override
    public boolean isAvailable() { return true; }
}

Use it:

notify.to(user)
    .via(Channel.custom("push"))
    .template("new-message")
    .send();

Spring Boot auto-discovers any NotificationChannel bean. No extra config needed.

Event Listeners + Spring Events

Monitor notification outcomes with the listener interface:

@Component
public class NotifyMonitor implements NotificationListener {

    @Override
    public void onSuccess(String channel, String template) {
        metrics.increment("notifications.sent." + channel);
    }

    @Override
    public void onFailure(String channel, String template, Exception error) {
        log.error("Failed on {}: {}", channel, error.getMessage());
        alertService.warn("Channel " + channel + " is failing");
    }

    @Override
    public void onScheduled(String channel, String recipient, Duration delay) {
        log.info("Scheduled for {} in {}", recipient, delay);
    }
}

Or use Spring Application Events (auto-configured):

@Component
public class NotificationEventHandler {

    @EventListener
    public void onSent(NotificationSentEvent event) {
        log.info("Sent via {} to {}", event.getChannel(), event.getRecipient());
    }

    @EventListener
    public void onFailed(NotificationFailedEvent event) {
        log.error("Failed: {}", event.getError().getMessage());
    }
}

Named Recipients

Send notifications to multiple destinations per channel using named aliases. Instead of one hardcoded webhook URL or chat ID, configure as many as you need:

Configure in application.yml:

notify:
  channels:
    discord:
      webhook-url: ${DISCORD_DEFAULT}      # default destination
      username: NotifyHub
      avatar-url: https://example.com/logo.png
      recipients:
        alerts: https://discord.com/api/webhooks/111/aaa
        devops: https://discord.com/api/webhooks/222/bbb
        general: https://discord.com/api/webhooks/333/ccc

    slack:
      webhook-url: ${SLACK_DEFAULT}
      recipients:
        engineering: https://hooks.slack.com/services/XXX/YYY/ZZZ
        marketing: https://hooks.slack.com/services/AAA/BBB/CCC

    telegram:
      bot-token: ${TELEGRAM_BOT_TOKEN}
      chat-id: ${TELEGRAM_DEFAULT_CHAT}
      recipients:
        alerts: "-1001234567890"
        devops: "-1009876543210"

Use with the Java API:

// Send to a named alias
notify.to("alerts").via(DISCORD).content("Server is down!").send();
notify.to("engineering").via(SLACK).content("Deploy complete").send();
notify.to("devops").via(TELEGRAM).content("CPU at 95%").send();

// Send to default (no alias)
notify.to("user").via(DISCORD).content("Hello!").send();

// Pass a raw URL directly (no alias needed)
notify.to("https://discord.com/api/webhooks/444/ddd").via(DISCORD).content("Direct!").send();

Use with the MCP Server (AI Agents):

send_discord(recipient="alerts", body="Server is down!")
send_slack(recipient="engineering", body="Deploy complete")
send_telegram(recipient="devops", body="CPU at 95%")

Environment variables for MCP/Docker:

# Default webhook
NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL=https://discord.com/api/webhooks/111/aaa

# Named recipients (RECIPIENTS_<NAME>)
NOTIFY_CHANNELS_DISCORD_RECIPIENTS_ALERTS=https://discord.com/api/webhooks/222/bbb
NOTIFY_CHANNELS_DISCORD_RECIPIENTS_DEVOPS=https://discord.com/api/webhooks/333/ccc

# Same pattern for all channels
NOTIFY_CHANNELS_SLACK_RECIPIENTS_ENGINEERING=https://hooks.slack.com/services/XXX
NOTIFY_CHANNELS_TELEGRAM_RECIPIENTS_ALERTS=-1001234567890
NOTIFY_CHANNELS_TEAMS_RECIPIENTS_GENERAL=https://outlook.office.com/webhook/XXX
NOTIFY_CHANNELS_GOOGLE_CHAT_RECIPIENTS_TEAM=https://chat.googleapis.com/v1/spaces/XXX

Resolution order: alias match in recipients map > raw URL/value passthrough > default from config.

Supported on: Discord, Slack, Telegram, Teams, Google Chat.

Message Queue (RabbitMQ / Kafka)

Decouple notification sending with async message queues. NotifyHub provides two modules:

RabbitMQ

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-queue-rabbitmq</artifactId>
    <version>1.0.0</version>
</dependency>

spring.rabbitmq.host: localhost
spring.rabbitmq.port: 5672

notify.queue.rabbitmq:
  enabled: true
  queue-name: notifyhub-notifications
  exchange-name: notifyhub-exchange
  routing-key: notification
  consumer:
    enabled: true
    concurrency: 1
    max-concurrency: 5

@Autowired RabbitNotificationProducer producer;

// Enqueue for async delivery
producer.enqueue(QueuedNotification.builder()
    .recipient("user@example.com")
    .channelName("email")
    .subject("Welcome!")
    .templateName("welcome")
    .params(Map.of("name", "Gabriel"))
    .build());
// Consumer picks it up and sends via NotifyHub automatically

Apache Kafka

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-queue-kafka</artifactId>
    <version>1.0.0</version>
</dependency>

spring.kafka.bootstrap-servers: localhost:9092

notify.queue.kafka:
  enabled: true
  topic: notifyhub-notifications
  consumer:
    enabled: true
    group-id: notifyhub-group
    concurrency: 1

@Autowired KafkaNotificationProducer producer;

// Same API as RabbitMQ — just different transport
producer.enqueue(QueuedNotification.builder()
    .recipient("+5548999999999")
    .channelName("sms")
    .rawContent("Your code is 1234")
    .priority("URGENT")
    .build());

Both modules support: templates, priority, deduplication keys, delivery tracking, and phone number routing for SMS/WhatsApp.

Circuit Breaker

Per-channel circuit breaker prevents cascading failures. If a channel fails repeatedly, the circuit opens and short-circuits further attempts:

// Without Spring Boot
NotifyHub notify = NotifyHub.builder()
    .channel(emailChannel)
    .circuitBreaker(CircuitBreakerConfig.defaults()) // 5 failures → open for 30s
    .build();

// Custom thresholds
NotifyHub notify = NotifyHub.builder()
    .channel(emailChannel)
    .circuitBreaker(CircuitBreakerConfig.custom()
        .failureThreshold(3)
        .openDuration(Duration.ofMinutes(1))
        .windowSize(Duration.ofSeconds(30))
        .build())
    .build();

# Spring Boot
notify:
  circuit-breaker:
    enabled: true
    failure-threshold: 5
    open-duration: 30s
    window-size: 60s

States: CLOSED (normal) → OPEN (rejecting) → HALF_OPEN (testing recovery). The health endpoint includes circuit breaker status per channel.

Bulkhead (Concurrency Isolation)

Limit concurrent sends per channel to prevent resource exhaustion:

NotifyHub notify = NotifyHub.builder()
    .channel(emailChannel)
    .bulkhead(BulkheadConfig.defaults())       // 10 concurrent per channel
    .bulkhead(BulkheadConfig.perChannel(5))    // or custom limit
    .build();

Multi-Channel Orchestration

Build escalation workflows that promote through channels if the user doesn't engage:

notify.to(user)
    .orchestrate()
    .first(Channel.EMAIL)
        .template("order-update")
    .ifNoOpen(Duration.ofHours(24))
    .then(Channel.PUSH)
        .content("You have an unread order update")
    .ifNoOpen(Duration.ofHours(48))
    .then(Channel.SMS)
        .content("Order update waiting — check your email")
    .execute();

Each step waits for the specified duration before escalating to the next channel.

A/B Testing

Built-in deterministic A/B testing for notifications. Variant assignment is hash-based (SHA-256) — the same recipient always gets the same variant:

notify.to(user)
    .via(Channel.EMAIL)
    .subject("Welcome!")
    .abTest("welcome-experiment")
        .variant("control", b -> b.template("welcome-v1"))
        .variant("new-design", b -> b.template("welcome-v2"))
        .split(50, 50);

Supports any number of variants with weighted splits. Deterministic hashing ensures consistent experiences across sends.

Cron Scheduling

Schedule recurring notifications with cron expressions:

ScheduledNotification job = notify.to(user)
    .via(Channel.EMAIL)
    .template("weekly-digest")
    .cron("0 9 * * MON"); // Every Monday at 9 AM

Supports standard 5-field cron syntax: minute, hour, day-of-month, month, day-of-week. Includes ranges, lists, steps, and named days/months.

Quiet Hours

Respect user preferences for notification timing:

public class User implements Notifiable {
    @Override
    public QuietHours getQuietHours() {
        return QuietHours.between(
            LocalTime.of(22, 0),  // 10 PM
            LocalTime.of(8, 0),   // 8 AM
            ZoneId.of("America/Sao_Paulo")
        );
    }

    @Override
    public Set<Channel> getOptedOutChannels() {
        return Set.of(Channel.SMS); // User opted out of SMS
    }
}

Notifications sent during quiet hours are delayed to the next allowed window. Opted-out channels are silently skipped.

Testing Utilities

TestNotifyHub provides a test-friendly wrapper with capturing channels for all built-in channel types:

@Test
void shouldSendWelcomeEmail() {
    TestNotifyHub test = TestNotifyHub.create();

    test.to("user@test.com")
        .via(Channel.EMAIL)
        .subject("Welcome")
        .content("Hello!")
        .send();

    assertThat(test.sent()).hasSize(1);
    assertThat(test.sent("email").get(0).subject()).isEqualTo("Welcome");
}

No mocking needed — TestNotifyHub captures all notifications in memory for assertions. Call test.reset() between tests.

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Supported Channels

	Channel	Provider	Module
	Email	SMTP (Gmail, SES, Outlook, any)	notify-email
📱	SMS	Twilio	notify-sms
	WhatsApp	Twilio	notify-sms
	Slack	Incoming Webhooks	notify-slack
	Telegram	Bot API	notify-telegram
	Discord	Webhooks	notify-discord
👥	Microsoft Teams	Incoming Webhooks	notify-teams
	Push (FCM)	Firebase Cloud Messaging	notify-push-firebase
🔗	Webhook	Any HTTP endpoint	notify-webhook
	WebSocket	JDK WebSocket (java.net.http)	notify-websocket
	Google Chat	Webhooks	notify-google-chat
	Twitter/X	API v2 (OAuth 1.0a)	notify-twitter
💼	LinkedIn	REST API (OAuth 2.0)	notify-linkedin
	Notion	API (Integration Token)	notify-notion
	Twitch	Helix API (OAuth 2.0 auto-refresh)	notify-twitch
	YouTube	Data API v3 (OAuth auto-refresh)	notify-youtube
	Instagram	Meta Graph API	notify-instagram
📧	SendGrid	SendGrid API (delivery tracking)	notify-sendgrid
	TikTok Shop	TikTok Shop API (HMAC-SHA256)	notify-tiktok-shop
	Facebook	Graph API (Page + Messenger)	notify-facebook
	WhatsApp Cloud	Meta Cloud API (direct, no Twilio)	notify-whatsapp
☁️	AWS SNS	AWS SDK v2	notify-aws-sns
	Mailgun	Mailgun REST API	notify-mailgun
	PagerDuty	Events API v2	notify-pagerduty
	Kick	Public API	notify-kick
➕	Custom	Any — implement one interface	notify-core

---

Admin Dashboard

NotifyHub includes a built-in admin dashboard for monitoring your notification system.

notify:
  admin:
    enabled: true

<dependency>
    <groupId>io.github.gabrielbbaldez</groupId>
    <artifactId>notify-admin</artifactId>
    <version>1.0.0</version>
</dependency>

Access at /notify-admin to see:

• Dashboard — metric cards (sent/failed/pending/DLQ/channels/contacts), recent activity feed, system status grid, registered channels
• Analytics — Chart.js charts with send volume, channel distribution, success rate, hourly heatmap
• Tracking — delivery receipts with channel filter and status badges
• Dead Letter Queue — failed notifications with error details and remove action
• Channels — status of each registered channel with health indicators
• Audit Log — complete history of all notification events with event type filter
• Audiences — manage contacts and audience segments with tag-based filtering
• Status Webhook — real-time HTTP callback configuration and delivery history

Dark/light theme toggle included — persists across pages via localStorage.

---

Spring Boot Integration

Micrometer Metrics

Auto-configured when Micrometer is on the classpath:

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-core</artifactId>
</dependency>

Exposes counters and gauges via the unified EventBus:

• notifyhub.notifications.sent (tags: channel)
• notifyhub.notifications.failed (tags: channel)
• notifyhub.notifications.retried (tags: channel)
• notifyhub.notifications.rate_limited (tags: channel)
• notifyhub.notifications.deduped (tags: channel)
• notifyhub.notifications.circuit_opened (tags: channel)
• notifyhub.notifications.circuit_closed (tags: channel)
• notifyhub.notifications.send_duration (timer, tags: channel)

Actuator Health Check

Auto-configured when Spring Boot Actuator is on the classpath:

GET /actuator/health/notifyhub

{
  "status": "UP",
  "details": {
    "email": { "status": "UP", "circuitBreaker": "CLOSED" },
    "slack": { "status": "UP", "circuitBreaker": "CLOSED" },
    "totalChannels": 2,
    "availableChannels": 2
  }
}

Status: UP (all channels available), DEGRADED (some down), DOWN (all down). When circuit breaker is configured, each channel also reports its circuit state.

Actuator Info

GET /actuator/info

{
  "notifyhub": {
    "version": "1.0.0",
    "channels": ["email", "slack", "teams"],
    "tracking.enabled": true,
    "dlq.enabled": true
  }
}

OpenTelemetry Tracing

Auto-configured when Micrometer Observation and an OTel bridge are on the classpath. Add these dependencies to export distributed traces via OTLP:

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-tracing-bridge-otel</artifactId>
</dependency>
<dependency>
    <groupId>io.opentelemetry</groupId>
    <artifactId>opentelemetry-exporter-otlp</artifactId>
</dependency>

Configure the OTLP endpoint in application.yml:

management:
  tracing:
    sampling:
      probability: 1.0       # 100% sampling (adjust for production)
  otlp:
    tracing:
      endpoint: http://localhost:4318/v1/traces

Creates observations (spans):

• notifyhub.send (tags: channel, template, outcome)
• notifyhub.schedule (tags: channel, outcome)

Compatible with Jaeger, Zipkin, Grafana Tempo, Datadog, and any OTLP-compatible collector.

Webhook HMAC Signing

The Status Webhook listener supports HMAC-SHA256 request signing for security. When configured, every webhook POST includes a X-NotifyHub-Signature header that your server can use to verify the request came from NotifyHub.

notify:
  status-webhook:
    url: https://your-server.com/webhook
    signing-secret: ${WEBHOOK_SECRET}   # any secret string

Each request includes the header:

X-NotifyHub-Signature: sha256=<hex-encoded HMAC-SHA256 of request body>

Verify in your server:

Mac mac = Mac.getInstance("HmacSHA256");
mac.init(new SecretKeySpec(secret.getBytes(), "HmacSHA256"));
String expected = "sha256=" + HexFormat.of().formatHex(mac.doFinal(body.getBytes()));
boolean valid = MessageDigest.isEqual(expected.getBytes(), signature.getBytes());

---

Configuration Reference

Full application.yml with all options:

notify:
  channels:
    email:
      host: smtp.gmail.com
      port: 587
      username: ${GMAIL_USER}
      password: ${GMAIL_PASS}
      from: noreply@myapp.com
      from-name: MyApp
      tls: true
      ssl: false

    sms:
      account-sid: ${TWILIO_SID}
      auth-token: ${TWILIO_TOKEN}
      from-number: "+1234567890"

    whatsapp:
      account-sid: ${TWILIO_SID}
      auth-token: ${TWILIO_TOKEN}
      from-number: "+14155238886"

    slack:
      webhook-url: ${SLACK_WEBHOOK}
      recipients:                          # named aliases (optional)
        engineering: https://hooks.slack.com/services/XXX
        marketing: https://hooks.slack.com/services/YYY

    telegram:
      bot-token: ${TELEGRAM_BOT_TOKEN}
      chat-id: ${TELEGRAM_CHAT_ID}
      recipients:                          # named aliases (optional)
        alerts: "-1001234567890"
        devops: "-1009876543210"

    discord:
      webhook-url: ${DISCORD_WEBHOOK}
      username: NotifyHub
      avatar-url: https://example.com/logo.png
      recipients:                          # named aliases (optional)
        alerts: https://discord.com/api/webhooks/111/aaa
        devops: https://discord.com/api/webhooks/222/bbb

    teams:
      webhook-url: ${TEAMS_WEBHOOK}
      recipients:                          # named aliases (optional)
        general: https://outlook.office.com/webhook/XXX

    push:
      credentials-path: ${FIREBASE_CREDENTIALS}
      project-id: ${FIREBASE_PROJECT_ID}

    webhooks:
      - name: pagerduty
        url: https://events.pagerduty.com/v2/enqueue
        headers:
          Authorization: "Token ${PAGERDUTY_TOKEN}"
        payload-template: '{"summary":"{{content}}"}'

    websocket:
      uri: wss://echo.example.com/ws
      timeout-ms: 10000
      reconnect-enabled: true
      reconnect-delay-ms: 5000
      max-reconnect-attempts: 3
      headers:
        Authorization: "Bearer ${WS_TOKEN}"
      message-format: '{"type":"notification","content":"{{content}}"}'

    google-chat:
      webhook-url: ${GOOGLE_CHAT_WEBHOOK}
      timeout-ms: 10000
      recipients:                          # named aliases (optional)
        team-a: https://chat.googleapis.com/v1/spaces/XXX/messages?key=YYY
        team-b: https://chat.googleapis.com/v1/spaces/ZZZ/messages?key=WWW

  retry:
    max-attempts: 3
    strategy: exponential

  rate-limit:
    enabled: true
    max-requests: 100
    window: 1m
    channels:
      email:
        max-requests: 50
        window: 1m

  tracking:
    enabled: true
    type: memory         # memory | jpa
    dlq-enabled: true

  deduplication:
    enabled: true
    ttl: 24h
    strategy: content-hash  # content-hash | explicit-key | both

  admin:
    enabled: true

---

Without Spring Boot

NotifyHub works without Spring — use the builder directly:

NotifyHub notify = NotifyHub.builder()
    .templateEngine(new MustacheTemplateEngine())
    .channel(new SmtpEmailChannel(
        SmtpConfig.builder()
            .host("smtp.gmail.com").port(587)
            .username("user@gmail.com").password("app-password")
            .from("noreply@myapp.com").tls(true)
            .build()
    ))
    .channel(new SlackChannel(
        SlackConfig.builder()
            .webhookUrl("https://hooks.slack.com/services/XXX/YYY/ZZZ")
            .recipients(Map.of("engineering", "https://hooks.slack.com/services/AAA/BBB/CCC"))
            .build()
    ))
    .channel(new TeamsChannel(
        TeamsConfig.builder()
            .webhookUrl("https://outlook.office.com/webhook/XXX/YYY/ZZZ")
            .build()
    ))
    .channel(new WebhookChannel(
        WebhookConfig.builder()
            .name("pagerduty")
            .url("https://events.pagerduty.com/v2/enqueue")
            .payloadTemplate("{\"summary\":\"{{content}}\"}")
            .build()
    ))
    .channel(new WebSocketChannel(
        WebSocketConfig.builder()
            .uri("wss://echo.example.com/ws")
            .messageFormat("{\"text\":\"{{content}}\"}")
            .build()
    ))
    .channel(new GoogleChatChannel(
        GoogleChatConfig.builder()
            .webhookUrl("https://chat.googleapis.com/v1/spaces/XXX/messages?key=YYY")
            .build()
    ))
    .deduplicationStore(new InMemoryDeduplicationStore(Duration.ofHours(24)))
    .defaultRetryPolicy(RetryPolicy.exponential(3))
    .rateLimiter(new TokenBucketRateLimiter(
        RateLimitConfig.perMinute(100)))
    .deadLetterQueue(new InMemoryDeadLetterQueue())
    .tracker(new InMemoryNotificationTracker())
    .circuitBreaker(CircuitBreakerConfig.defaults())
    .bulkhead(BulkheadConfig.defaults())
    .build();

// Sync
notify.to("user@email.com")
    .via(Channel.EMAIL)
    .subject("Hello!")
    .content("Welcome to the app!")
    .send();

// Async
notify.to("#general")
    .via(Channel.SLACK)
    .content("Deploy complete!")
    .sendAsync();

// Tracked
DeliveryReceipt receipt = notify.to(user)
    .via(Channel.EMAIL)
    .content("Invoice attached")
    .sendTracked();

// Scheduled
notify.to(user)
    .via(Channel.EMAIL)
    .content("Reminder!")
    .schedule(Duration.ofMinutes(30));

// Batch
notify.toAll(List.of("a@test.com", "b@test.com"))
    .via(Channel.EMAIL)
    .template("announcement")
    .send();

Only notify-core + channel modules needed. No Spring dependency.

---

MCP Server (AI Agents)

NotifyHub includes an MCP (Model Context Protocol) server that exposes all notification channels as tools for AI agents like Claude Desktop, Claude Code, Cursor, and any MCP-compatible client.

How it works

The notify-mcp module is a standalone Java application that communicates via STDIO using the JSON-RPC protocol. AI agents discover the available tools and can send notifications through any configured channel.

Setup

1. Build the MCP server:

mvn clean package -pl notify-mcp -am -DskipTests

2. Configure in Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "notify-hub": {
      "command": "java",
      "args": ["-jar", "path/to/notify-mcp-1.0.0.jar"],
      "env": {
        "NOTIFY_CHANNELS_EMAIL_HOST": "smtp.gmail.com",
        "NOTIFY_CHANNELS_EMAIL_PORT": "587",
        "NOTIFY_CHANNELS_EMAIL_USERNAME": "you@gmail.com",
        "NOTIFY_CHANNELS_EMAIL_PASSWORD": "app-password",
        "NOTIFY_CHANNELS_SLACK_WEBHOOK_URL": "https://hooks.slack.com/...",
        "NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL": "https://discord.com/api/webhooks/..."
      }
    }
  }
}

Or for Claude Code (.mcp.json in project root):

{
  "mcpServers": {
    "notify-hub": {
      "command": "java",
      "args": ["-jar", "path/to/notify-mcp-1.0.0.jar"],
      "env": {
        "NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL": "https://discord.com/api/webhooks/..."
      }
    }
  }
}

Available MCP Tools

Tool	Description	Required Params
send_notification	Send via any channel (generic)	channel, recipient, body or template
send_email	Send email	to, body or template
send_sms	Send SMS via Twilio	phone, body or template
send_slack	Send to Slack channel	recipient, body or template
send_telegram	Send via Telegram Bot	recipient, body or template
send_discord	Send to Discord channel	recipient, body or template
send_whatsapp	Send WhatsApp via Twilio	phone, body or template
send_teams	Send to Microsoft Teams	recipient, body or template
send_google_chat	Send to Google Chat	recipient, body or template
send_push	Send push via Firebase	push_token, body
send_twitter	Post a tweet on Twitter/X	body or template
send_linkedin	Publish a post on LinkedIn	body or template
send_notion	Create a page in Notion	recipient, body or template
send_twitch	Send Twitch chat message + polls	recipient, body or template
send_youtube	Send YouTube live chat message	recipient, body or template
send_instagram	Send Instagram DM or feed post	recipient, body or template
send_multi_channel	Send to multiple channels	channels[], recipient, body or template
send_batch	Send to multiple recipients at once	recipients[], channel, body or template
send_to_audience	Send to a named audience	audience, channel, body or template
list_channels	List configured channels	(none)
list_delivery_receipts	Query delivery history	(none)
list_dead_letters	View failed notifications (DLQ)	(none)
create_contact	Create a contact with tags	name
list_contacts	List contacts (filter by tag)	(none)
create_audience	Create audience with tag filters	name, tags[]
list_audiences	List audiences with contact counts	(none)
get_analytics	Delivery stats by channel/status	(none)
send_tiktok_shop	Send TikTok Shop notification	recipient, body or template
send_facebook	Send Facebook page post or Messenger DM	recipient, body or template
check_email_status	Check SendGrid email delivery status	message_id
schedule_notification	Schedule a notification for later delivery	channel, recipient, body, send_at
list_scheduled_notifications	List all scheduled notifications	(none)
cancel_scheduled_notification	Cancel a pending scheduled notification	notification_id

All send tools optionally accept: subject, template, params, priority.

Usage example (from an AI agent)

Once configured, you can simply ask your AI agent:

"Send a Discord message to #alerts saying the deploy is complete"

The agent will call the send_discord tool with the appropriate parameters.

Docker

Run the MCP server without Java installed — only Docker required:

# Build
docker build -t notifyhub-mcp .

# Run with Discord
docker run -i --rm \
  -e NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL="https://discord.com/api/webhooks/..." \
  -e NOTIFY_CHANNELS_DISCORD_USERNAME="NotifyHub" \
  gabrielbbal10/notifyhub-mcp

# Run with multiple Discord channels + Email
docker run -i --rm \
  -e NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL="https://discord.com/api/webhooks/..." \
  -e NOTIFY_CHANNELS_DISCORD_USERNAME="NotifyHub" \
  -e NOTIFY_CHANNELS_DISCORD_RECIPIENTS_ALERTS="https://discord.com/api/webhooks/111/aaa" \
  -e NOTIFY_CHANNELS_DISCORD_RECIPIENTS_DEVOPS="https://discord.com/api/webhooks/222/bbb" \
  -e NOTIFY_CHANNELS_EMAIL_HOST="smtp.gmail.com" \
  -e NOTIFY_CHANNELS_EMAIL_PORT="587" \
  -e NOTIFY_CHANNELS_EMAIL_USERNAME="you@gmail.com" \
  -e NOTIFY_CHANNELS_EMAIL_PASSWORD="app-password" \
  -e NOTIFY_CHANNELS_EMAIL_FROM="you@gmail.com" \
  gabrielbbal10/notifyhub-mcp

Configure in Claude Code (.mcp.json):

{
  "mcpServers": {
    "notify-hub": {
      "command": "docker",
      "args": ["run", "-i", "--rm",
        "-e", "NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL=https://discord.com/api/webhooks/...",
        "-e", "NOTIFY_CHANNELS_DISCORD_USERNAME=NotifyHub",
        "-e", "NOTIFY_CHANNELS_DISCORD_RECIPIENTS_ALERTS=https://discord.com/api/webhooks/111/aaa",
        "gabrielbbal10/notifyhub-mcp"
      ]
    }
  }
}

Docker REST API

Run a full REST API with Swagger UI — no Java required, just Docker:

docker run -d -p 8080:8080 \
  -e NOTIFY_CHANNELS_EMAIL_USERNAME=you@gmail.com \
  -e NOTIFY_CHANNELS_EMAIL_PASSWORD=your-app-password \
  -e NOTIFY_CHANNELS_EMAIL_FROM=you@gmail.com \
  gabrielbbal10/notifyhub-api:latest

Open http://localhost:8080/swagger-ui.html for interactive API docs.

Environment variables — same for both MCP and API images, add only the channels you need:

Channel	Variable	Required	Example
Email	NOTIFY_CHANNELS_EMAIL_HOST	No (default: smtp.gmail.com)	smtp.gmail.com
	NOTIFY_CHANNELS_EMAIL_PORT	No (default: 587)	587
	NOTIFY_CHANNELS_EMAIL_USERNAME	Yes (for email)	you@gmail.com
	NOTIFY_CHANNELS_EMAIL_PASSWORD	Yes (for email)	abcd efgh ijkl mnop (App Password)
	NOTIFY_CHANNELS_EMAIL_FROM	Yes (for email)	you@gmail.com
Discord	NOTIFY_CHANNELS_DISCORD_WEBHOOK_URL	Yes (for discord)	https://discord.com/api/webhooks/...
	NOTIFY_CHANNELS_DISCORD_USERNAME	No	NotifyHub
	NOTIFY_CHANNELS_DISCORD_AVATAR_URL	No	https://example.com/avatar.png
	`NOTI