MCP LSP — Code Intelligence Server

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A Model Context Protocol (MCP) stdio server that wraps language servers to expose a safe, read-oriented code-intelligence tool surface for coding agents. Supports TypeScript, JavaScript, Python, Go, and Rust — 59 tools across navigation, diagnostics, refactoring, deep understanding, hierarchy, lifecycle, and operations.

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Table of Contents

• Quick Start
• Prerequisites
• Installation
• Configuration
• Architecture
• API Reference
• Error Handling
• Safety Model
• Development
• Testing
• Supported Languages
• Troubleshooting
• Changelog
• License

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Quick Start

# Prerequisites: install language servers
npm install -g typescript-language-server pyright
# Go and Rust: install gopls and rust-analyzer via your package manager

# Clone and install
git clone https://github.com/beruang/lsp-mcp.git
cd lsp-mcp
pnpm install

# Build
pnpm run build

# Point at a workspace and start
WORKSPACE_PATH=/path/to/your/project node dist/index.js

Connect any MCP client to the server's stdio transport.

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Prerequisites

Dependency	Version	Purpose
Node.js	>= 20	Runtime
pnpm	—	Package management
typescript-language-server	—	TypeScript/JavaScript LSP backend
pyright-langserver	—	Python LSP backend
gopls	—	Go LSP backend
rust-analyzer	—	Rust LSP backend

Language servers must be on $PATH. The server checks availability via lsp_list_supported_languages.

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Installation

pnpm install

Dependencies: @modelcontextprotocol/sdk, vscode-jsonrpc, vscode-languageserver-types, zod, diff.

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Configuration

Environment Variables

Variable	Required	Default	Description
WORKSPACE_PATH	No	process.cwd()	Absolute path to the workspace root

Runtime Config (V4)

Variable	Default	Description
LSP_MAX_REFERENCES	200	Max references returned
LSP_MAX_WORKSPACE_SYMBOLS	100	Max workspace symbols
LSP_MAX_DIAGNOSTICS	500	Max diagnostics
LSP_MAX_COMPLETION_ITEMS	50	Max completion items
LSP_MAX_CHANGED_FILES	100	Max files in rename preview
LSP_MAX_EDITS	1000	Max edits in workspace edit
LSP_MAX_CONTEXT_CHARACTERS	20000	Max context characters
LSP_TIMEOUT_HOVER_MS	3000	Hover timeout
LSP_TIMEOUT_DEFINITION_MS	5000	Definition timeout
LSP_TIMEOUT_REFERENCES_MS	10000	References timeout
LSP_REQUEST_LOG_MAX_ENTRIES	500	Request log ring buffer size
LSP_RAW_REQUEST_ENABLED	false	Enable debug raw request tool
LSP_VERBOSE_LOGGING	false	Verbose logging

Use lsp_get_config to inspect effective configuration and lsp_update_runtime_config to adjust limits, timeouts, cache TTLs, and debug flags at runtime (in-memory only).

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Architecture

src/
├── index.ts                          # Entry point — MCP server bootstrap
├── config/
│   ├── languageServers.ts            # Language server registry
│   ├── defaults.ts                   # Default runtime config values
│   ├── envConfig.ts                  # Environment variable parsing
│   └── runtimeConfig.ts              # In-memory config merge + validation
├── lsp/
│   ├── LspClient.ts                  # LSP connection: spawn, initialize, request, shutdown
│   ├── LspClientManager.ts           # Per-language client pool + state queries
│   ├── LspState.ts                   # 8-state machine with validated transitions
│   ├── capabilities.ts               # Server capabilities extraction
│   ├── diagnosticsCache.ts           # publishDiagnostics notification cache
│   ├── documentStore.ts              # didOpen/didChange state tracking
│   └── normalize.ts                  # LSP → normalized shape converters
├── mcp/
│   ├── registerTools.ts              # All 59 MCP tool registrations
│   ├── toolErrors.ts                 # Structured error envelope
│   └── schemas.ts                    # Zod schemas
├── navigation/                       # V3: declaration, typeDef, implementation, signatureHelp, completion
├── hierarchy/                        # V3: call hierarchy + type hierarchy (prepare, incoming/outgoing, super/subtypes)
├── workspaceEdit/                    # V2: parse, validate, preview workspace edits
├── codeActions/                      # V2: code action cache + normalization
├── diagnostics/                      # V2: snapshot store, compare, wait-for-diagnostics
├── context/                          # V3: enclosing symbol, symbol context, file outline
├── analysis/                         # V3: change impact, fix candidates, explain diagnostics
├── formatting/                       # V2: format + range format preview
├── refactor/                         # V2: prepare rename, organize imports
├── composite/                        # V1: diagnostics summary, inspect symbol
├── diff/                             # V1: applyTextEdits, workspaceEditToDiff
├── semantic/                         # V3: fixDiagnosticCandidates, explainDiagnostics, analyzeChangeImpact
├── documents/                        # V4: open, close, sync, save, list documents
├── ops/                              # V4: server status, restart, shutdown, readiness, liveness, workspace status
├── observability/                    # V4: request tracker, request log
├── cache/                            # V4: cache status + selective clearing
├── debug/                            # V4: raw request (disabled by default, method denylist)
├── safety/
│   ├── paths.ts                      # Workspace containment check
│   └── limits.ts                     # Truncation caps and timeouts
└── utils/
    ├── asyncTimeout.ts               # Promise race with timeout
    ├── uri.ts                        # URI ↔ path conversion
    ├── symbols.ts                    # Symbol kind normalization
    ├── ids.ts                        # ID generation
    ├── text.ts                       # Text utilities
    └── time.ts                       # Time utilities

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API Reference

Every tool returns either a success payload or a structured error:

{
  "error": {
    "code": "path_outside_workspace",
    "message": "Human-readable description",
    "details": {}
  }
}

Navigation & Discovery

Tool	LSP Method	Description
lsp_hover	textDocument/hover	Type information and documentation at cursor
lsp_definition	textDocument/definition	Go-to-definition locations
lsp_references	textDocument/references	Find all references to a symbol
lsp_document_symbols	textDocument/documentSymbol	Symbol outline for a file
lsp_workspace_symbols	workspace/symbol	Workspace-wide symbol search
lsp_declaration	textDocument/declaration	Go-to-declaration
lsp_type_definition	textDocument/typeDefinition	Go-to-type-definition
lsp_implementation	textDocument/implementation	Find implementations

Diagnostics

Tool	Description
lsp_diagnostics	Cached diagnostics for a file or workspace-wide
lsp_diagnostics_summary	Grouped diagnostics with root-cause heuristic
lsp_wait_for_diagnostics	Wait for fresh diagnostics after a change
lsp_snapshot_diagnostics	Save a named diagnostic snapshot for comparison
lsp_compare_diagnostics	Diff two diagnostic snapshots
lsp_explain_diagnostics	Cluster diagnostics and identify root causes
lsp_fix_diagnostic_candidates	Multi-source fix suggestions (hover + code actions + definition)

Refactoring & Editing

Tool	LSP Method	Description
lsp_rename_preview	textDocument/rename	Preview rename via WorkspaceEdit + unified diff
lsp_prepare_rename	textDocument/prepareRename	Check if rename is valid at a position
lsp_code_actions_preview	textDocument/codeAction	Preview code actions with diffs
lsp_resolve_code_action	codeAction/resolve	Resolve a cached code action
lsp_format_preview	textDocument/formatting	Preview formatting with diff
lsp_range_format_preview	textDocument/rangeFormatting	Preview range formatting with diff
lsp_organize_imports_preview	textDocument/organizeImports	Preview import organization with diff
lsp_workspace_edit_preview	—	Preview any WorkspaceEdit + unified diff
lsp_validate_workspace_edit	—	Validate WorkspaceEdit safety

Deep Understanding

Tool	LSP Method	Description
lsp_signature_help	textDocument/signatureHelp	Function signature at call site
lsp_completion	textDocument/completion	Code completion suggestions
lsp_inspect_symbol	composite	Aggregate: hover + definition + refs + risk hints
lsp_symbol_context	composite	Surrounding symbols at a position
lsp_enclosing_symbol	composite	Innermost enclosing symbol
lsp_file_outline	composite	File-level symbol outline

Hierarchy & Impact

Tool	LSP Method	Description
lsp_prepare_call_hierarchy	textDocument/prepareCallHierarchy	Prepare call hierarchy for a symbol
lsp_incoming_calls	callHierarchy/incomingCalls	Who calls this symbol
lsp_outgoing_calls	callHierarchy/outgoingCalls	What this symbol calls
lsp_prepare_type_hierarchy	textDocument/prepareTypeHierarchy	Prepare type hierarchy
lsp_supertypes	typeHierarchy/supertypes	Super-types of a symbol
lsp_subtypes	typeHierarchy/subtypes	Sub-types of a symbol
lsp_analyze_change_impact	composite	Cross-file impact analysis for a proposed change

Server Lifecycle

Tool	Description
lsp_server_status	Runtime status for all configured language servers
lsp_restart_server	Restart a language server (reopens docs, clears diagnostics)
lsp_shutdown_server	Graceful shutdown with timeout
lsp_list_supported_languages	Configured languages, extensions, commands, binary availability
lsp_get_capabilities	Normalized LSP capabilities per language

Document Lifecycle

Tool	LSP Method	Description
lsp_open_document	textDocument/didOpen	Register a document with the LSP server
lsp_close_document	textDocument/didClose	Unregister a document
lsp_sync_document	textDocument/didChange	Notify LSP of content changes
lsp_save_document	textDocument/didSave	Notify LSP of a save
lsp_list_open_documents	—	All currently tracked open documents

Health

Tool	Description
lsp_health_check	Server health and per-language LSP capabilities
lsp_readiness	Workspace + language server availability check
lsp_liveness	Fast liveness check + optional memory stats

Observability & Cache

Tool	Description
lsp_request_log	LSP request history with filtering
lsp_clear_request_log	Clear request log entries
lsp_cache_status	Entry counts for all internal caches
lsp_clear_caches	Selective or full cache clearing

Configuration

Tool	Description
lsp_get_config	Effective config (defaults → env → runtime overrides)
lsp_update_runtime_config	In-memory config updates (limits, timeouts, caches, debug)

Debug

Tool	Description
lsp_raw_request	Raw LSP request with method denylist (disabled by default)

Multi-Workspace

Tool	Description
lsp_list_workspaces	Known workspaces (foundation)
lsp_workspace_status	Status for a specific workspace (foundation)

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Error Handling

Every tool returns errors in a uniform envelope:

{
  "error": {
    "code": "path_outside_workspace",
    "message": "Path is outside workspace: /etc/passwd",
    "details": {}
  }
}

Error Codes

Code	Trigger
path_outside_workspace	filePath does not resolve inside WORKSPACE_PATH
unsupported_language	File extension has no registered LSP server
file_not_found	File does not exist on disk
lsp_server_unavailable	Language server binary not on $PATH
lsp_server_not_initialized	Server not initialized
lsp_request_failed	LSP request returned an error
lsp_request_timeout	LSP request exceeded its deadline
lsp_capability_unsupported	Server does not support the capability
declaration_not_supported	Server lacks declaration provider
type_definition_not_supported	Server lacks type definition provider
implementation_not_supported	Server lacks implementation provider
signature_help_not_supported	Server lacks signature help provider
completion_not_supported	Server lacks completion provider
call_hierarchy_not_supported	Server lacks call hierarchy provider
call_hierarchy_item_not_found	Hierarchy item ID not found
call_hierarchy_item_expired	Hierarchy item TTL expired
type_hierarchy_not_supported	Server lacks type hierarchy provider
type_hierarchy_item_not_found	Type hierarchy item ID not found
type_hierarchy_item_expired	Type hierarchy item TTL expired
change_impact_analysis_incomplete	Change impact partial results
diagnostic_not_found	Diagnostic index not found
invalid_config_key	Unknown config key in update
invalid_config_value	Invalid config value (e.g., negative limit)
immutable_config_key	Attempt to change workspacePath at runtime
server_not_found	Language not configured
restart_rate_limited	Too many restarts in window
raw_request_disabled	Debug tool is disabled
method_denied	LSP method blocked by denylist
document_not_found	Document not in open documents store

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Safety Model

The server is designed for read-oriented coding agents:

Guard	Mechanism
Workspace containment	Every file path validated against WORKSPACE_PATH
No file writes	All tools are read-only; lsp_rename_preview returns a diff but never applies edits
Result caps	All list results are truncated with configurable limits
Timeouts	Every LSP request has a per-method deadline
Structured errors	All errors use the uniform { error: { code, message, details } } envelope
Request log privacy	Logs method, duration, status — never full file contents (unless verbose logging explicitly enabled)
Method denylist	lsp_raw_request blocks workspace/applyEdit, workspace/executeCommand, and other dangerous methods
Restart rate limiting	Max 3 restarts per 60s per language
State machine validation	Invalid LSP state transitions are logged and rejected

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Development

pnpm run typecheck     # TypeScript type-check
pnpm run lint          # ESLint (zero warnings)
pnpm run lint:fix      # ESLint auto-fix
pnpm run dev           # Run with tsx (no build)
pnpm run build         # Build to dist/
pnpm run start         # Start built artifact

Pre-commit Hook

husky + lint-staged:

1. eslint --fix --max-warnings 0
2. pnpm run typecheck
3. pnpm run verify:decoupling

Conventions

• Module system: ESM ("type": "module", NodeNext)
• TypeScript: strict, target ES2022
• Testing: node --test + tsx
• Linting: ESLint with @typescript-eslint, zero-warnings policy

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Testing

pnpm test              # All unit tests
npm run test:safety    # Safety tests
npm run test:integration  # Integration tests (requires language servers)

Coverage

• 106+ tests across unit, integration, and safety suites
• 5 languages: TypeScript, JavaScript, Python, Go, Rust
• V1-V3 regression: all passing with every V4 change

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Supported Languages

Language	Extensions	Language Server	Language ID
TypeScript	.ts, .tsx	typescript-language-server --stdio	typescript
JavaScript	.js, .jsx	typescript-language-server --stdio	typescript
Python	.py	pyright-langserver --stdio	python
Go	.go	gopls	go
Rust	.rs	rust-analyzer	rust

Adding a language:

1. Entry in src/config/languageServers.ts
2. Binary on $PATH
3. Optional waitConfig in src/lsp/diagnosticsCache.ts

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Troubleshooting

lsp_server_unavailable

which typescript-language-server pyright-langserver gopls rust-analyzer
npm install -g typescript-language-server pyright

Use lsp_list_supported_languages to check binary availability at runtime.

path_outside_workspace

Set WORKSPACE_PATH to the project root. Symlinks are resolved before containment check.

No diagnostics

Diagnostics are cached from publishDiagnostics notifications. For cold cache, use lsp_diagnostics with workspaceWide: true to trigger a warm-up pass, or lsp_wait_for_diagnostics.

Stale diagnostics after external edit

Use lsp_sync_document to notify the LSP of changes, then lsp_wait_for_diagnostics. For bulk recovery, lsp_restart_server with reopenDocuments: true.

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Changelog

Version	Focus	Key Additions
V4	Production operations	Server lifecycle, document lifecycle, observability, cache, config, health, debug, multi-workspace (21 tools)
V3	Deep understanding	Hierarchy (call + type), declaration, type definition, implementation, signature help, completion, impact analysis (17 tools)
V2	Safe refactoring	Preview-first editing — rename, code actions, formatting, organize imports, diagnostics snapshots (11 tools)
V1	Semantic navigation	Hover, definition, references, symbols, diagnostics, rename preview, inspect (10 tools)

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License

MIT