io.github.carldaws/squiggles

squiggles

Let your agent see the squiggles you'd see in an IDE.

squiggles is an MCP server that bridges coding agents to Language Server Protocol (LSP) servers. Configure one or more LSP servers and squiggles exposes their features — diagnostics, go-to-definition, find references, rename, formatting, and more — as MCP tools. Servers start lazily on first tool use, so there's no startup cost for languages you don't touch.

Beyond the standard protocol, squiggles unlocks the custom superpowers each language server ships that editors rarely surface and agents otherwise never see: expanding a Rust macro, discovering Ruby tests, switching between a C++ source file and its header, fixing every import after moving a TypeScript file, running govulncheck through gopls.

Quick Start

claude mcp add squiggles -- npx -y squiggles

Then create a squiggles.yaml in your project root:

servers:
  typescript:
    command: ["typescript-language-server", "--stdio"]
    filePatterns: ["**/*.ts", "**/*.tsx", "**/*.js", "**/*.jsx"]

Configuration

squiggles looks for squiggles.yaml, squiggles.yml, .squiggles.yaml, or .squiggles.yml in the project root (the old mclsp.yaml names still work). Each server entry supports:

Field	Required	Description
command	Yes	Command to start the LSP server (string array)
filePatterns	Yes	Glob patterns for files this server handles
initializationOptions	No	Options passed to the LSP server on initialization
rootUri	No	Override the workspace root URI
env	No	Environment variables for the LSP server process

Multiple servers can be configured for different languages:

servers:
  typescript:
    command: ["typescript-language-server", "--stdio"]
    filePatterns: ["**/*.ts", "**/*.tsx", "**/*.js", "**/*.jsx"]
  rust:
    command: ["rust-analyzer"]
    filePatterns: ["**/*.rs"]
  ruby:
    command: ["ruby-lsp"]
    filePatterns: ["**/*.rb"]
  go:
    command: ["gopls"]
    filePatterns: ["**/*.go", "go.mod", "go.sum"]
  cpp:
    command: ["clangd"]
    filePatterns: ["**/*.c", "**/*.h", "**/*.cpp", "**/*.hpp"]

Tools

All standard LSP tools are registered and available when a matching server is configured.

Navigation: goto_definition, goto_type_definition, goto_implementation, goto_declaration, find_references

Inspection: hover, signature_help, document_symbols, workspace_symbols

Refactoring: code_actions, rename_prepare, rename, format

Hierarchy: call_hierarchy_incoming, call_hierarchy_outgoing, type_hierarchy

Always available: open_file, diagnostics

Position-based tools take file (relative path), line (1-indexed), and col (1-indexed). rename accepts apply: true to write the edit to disk instead of returning it; format always writes to disk. code_actions automatically passes the diagnostics overlapping the requested range, so quick fixes show up.

Server Extensions

The best language servers go far beyond the standard protocol, and this is where squiggles earns its keep: it subscribes to the custom methods and commands that IDE plugins use but agent harnesses ignore. Extension tools register automatically when a matching server is configured.

Ruby (ruby-lsp)

Tool	What it does
ruby_discover_tests	Discover test cases (Minitest, RSpec) in a file
ruby_go_to_relevant_file	Jump between implementation and test file
ruby_show_syntax_tree	Show the Prism AST for a file
ruby_dependencies	List project gem dependencies

TypeScript (typescript-language-server)

Tool	What it does
ts_go_to_source_definition	Go to the implementation, not the .d.ts declaration
ts_organize_imports	Sort and prune imports, written to disk
ts_rename_file	Fix every import after a file moves — move the file, then call this

typescript-language-server needs a typescript install it can find (usually the workspace's own). TypeScript 7 ships no tsserver.js, so keep typescript@5 in the workspace for now.

Rust (rust-analyzer)

Tool	What it does
rust_expand_macro	Show the code a macro invocation generates
rust_parent_module	Navigate to the parent module
rust_open_cargo_toml	Find the owning crate's Cargo.toml
rust_external_docs	Get docs.rs / rustdoc URLs for a symbol
rust_related_tests	Find tests covering a position
rust_view_syntax_tree	Show the syntax tree for a file
rust_runnables	List runnable targets (tests, binaries, doctests)
rust_reload_workspace	Reload Cargo metadata after editing Cargo.toml
rust_dependencies	List all crates in the dependency graph

Go (gopls)

Tool	What it does
go_list_known_packages	List packages importable from a file
go_list_imports	List a file's imports and its package
go_add_import	Add an import, written to disk
go_mod_tidy	Run go mod tidy
go_vulncheck	Run govulncheck against the module
go_modules	List modules under a directory

C/C++ (clangd)

Tool	What it does
clangd_switch_source_header	Jump between source and header
clangd_symbol_info	Get USR and symbol details
clangd_ast	Show the Clang AST for a range

When a server applies changes itself (organize imports, add import, rename file), squiggles receives the workspace edit and writes it to disk, keeping the server's view of the files in sync.

Contributing Extensions

To add extensions for a new language server, create a file in src/extensions/ (e.g. src/extensions/zig.ts):

import { executeCommand, type ServerExtension } from "./index.js";

const extensions: ServerExtension[] = [
  {
    name: "zls_something",
    description: "What this does",
    input: "position", // "none" | "file" | "position" | "custom"
    request: ({ uri, position }) => ({
      method: "zls/customMethod",
      params: { textDocument: { uri }, position },
    }),
  },
];

export default extensions;

request receives the opened file's URI, absolute path, and 0-indexed position, and returns the LSP request to send — use the executeCommand helper for servers that expose functionality as workspace/executeCommand commands. Register the module in src/extensions/index.ts under the server's binary name.

Migrating from mclsp

squiggles is the project formerly published as mclsp. Point your MCP config at npx -y squiggles and rename mclsp.yaml to squiggles.yaml — the old config names keep working, the tool names are unchanged.

License

MIT