io.github.IcyHot09/opengrok
MCP server bridging OpenGrok indices with AI for deep, instant context across massive codebases.
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OpenGrok MCP Server
MCP server bridging OpenGrok search engine with AI for instant context across massive codebases
📚 Table of Contents
Overview
💡 Self-Contained Architecture: The VS Code extension includes the MCP server pre-packaged. You don't need Python, external Node.js installations, or complex environment setups. Just install and go.
Installation
Option 1 — VS Code Extension (Recommended)
Install OpenGrok MCP from the VS Code Marketplace, or search "OpenGrok" in the Extensions panel.
The extension provides a visual configuration UI and manages the MCP server process automatically.
Option 2 — npm / npx
Global install:
npm install -g opengrok-mcp-server
opengrok-mcp setup # interactive wizard: URL, credentials, MCP client registration
Or run without installing:
npx opengrok-mcp-server setup
The wizard stores credentials securely in the OS keychain (macOS Keychain, Windows Credential Manager, Linux libsecret) with an encrypted file fallback for headless Linux.
Configuration Guide
-
Provide Connection Details:
- After installation, the Settings panel will launch.
- Input your OpenGrok endpoint, username, and password. Hit Save Settings. (Credentials are locked in your native OS keychain).
- The plugin verifies the connection instantly. On your first run, VS Code will ask you to Reload the Window to register the MCP tools.
- (Need to change this later? Use the
OpenGrok: Manage Configurationcommand or click the gear icon in the status bar).
-
Activate the MCP Source in Copilot:
- Launch the GitHub Copilot Chat window. Ensure you're using Agent mode.
- Click the paperclip/tools icon (
🔧) in the prompt box. - (If an Update Tools button appears, click it).
- Locate OpenGrok in the list, check the box, and confirm.
⚠️ Note that VS Code manages tool authorizations per workspace. If you open a different repository, you may need to re-check the OpenGrok box in Copilot.
CLI Commands (v7.0+)
| Command | Description |
|---|---|
npx opengrok-mcp-server setup | Interactive wizard: configures your MCP client and stores credentials securely |
opengrok-mcp status | Health check: validates connectivity and detects installed MCP clients. Reads config from ~/.claude.json, ~/.copilot/mcp-config.json, or Codex TOML when OPENGROK_BASE_URL is not in env |
opengrok-mcp --version | Print version and exit |
setup supports Claude Code CLI, GitHub Copilot CLI, and Codex CLI. VS Code is configured automatically by the extension — no CLI step needed. Credentials are stored in the OS keychain with an AES-256-GCM encrypted file fallback for headless/CI environments.
🔌 Third-Party Client Support
While tailored for VS Code, the integrated server logic runs perfectly with other agents natively supporting the MCP protocol, including:
Claude Desktop | Cursor IDE | Windsurf | Claude Code | Google Antigravity
👉 Refer to MCP_CLIENTS.md for configuration snippets and advanced daemon setups.
Prompting Examples
Talk to GitHub Copilot Chat naturally about your codebase:
Find the implementation of the render_pipeline function within the graphics engine project.
Retrieve the contents of /src/utils/math.cpp from line 450 to 520.
What is the definition of TextureManager? Please show me the header file declaration too.
Look for all places in the code where ThreadPool is instantiated or referenced.
Tool Reference
Primary Operations
| Tool Name | Purpose |
|---|---|
opengrok_search_code | General search utility (full-text, defs, refs, path, history). Supports file_type filtering. |
opengrok_find_file | Locate files by name or directory pattern. |
opengrok_get_file_content | Read source code (requires start_line and end_line for large files). |
opengrok_get_file_history | Retrieve commit history logs. |
opengrok_browse_directory | View folder structure and contained files. |
opengrok_list_projects | See all indexed repositories/projects. |
opengrok_get_file_annotate | See line-by-line git blame information. |
opengrok_get_file_symbols | Extract classes, functions, macros, and structs rapidly from a single file. |
opengrok_search_suggest | Get query autocomplete recommendations. |
🚀 Optimized Workflows (Compound Tools)
💡 These specialized tools merge multiple network requests into a single operation, reducing API chatter and cutting token usage by up to 90%.
| Compound Tool | Functionality Replaced | Efficiency Gain |
|---|---|---|
opengrok_get_symbol_context | 1) searches definition, 2) reads source, 3) fetches headers, 4) gets references | ~92% fewer tokens |
opengrok_search_and_read | 1) executes search, 2) immediately fetches surrounding code context | ~92% fewer tokens |
opengrok_batch_search | Combines 2-5 individual search queries; deduplicates file:line hits across queries | ~73% fewer tokens |
opengrok_index_health | Checks latency, backend connectivity, staleness score, and latency trend | Diagnostic utility |
(Note: The search functions support language filtering. Pass file_type as java, cxx, python, golang, etc.)
🔍 Investigation & Analysis Tools (v5.6+)
| Tool | Purpose |
|---|---|
opengrok_what_changed | Recent line changes grouped by commit — author, date, SHA, changed lines with context. Parameters: project, path, since_days |
opengrok_dependency_map | BFS traversal of #include/import chains up to configurable depth (1–3); directed graph with uses/used_by |
opengrok_search_pattern | Regex code search via regexp=true; returns file:line:content matches |
opengrok_blame | Git blame with line range (start_line/end_line); returns author, date, commit per line (v5.6+) |
opengrok_call_graph | Call chain tracing via OpenGrok API v2 /symbol/{name}/callgraph (requires OPENGROK_API_VERSION=v2) |
opengrok_get_file_diff | Unified diff between two revisions with full context lines — shows surrounding code so AI understands why a change was made; use opengrok_get_file_history to discover revision hashes |
🧠 Memory Tools (Code Mode only, v5.4+)
| Tool | Purpose |
|---|---|
opengrok_memory_status | Shows both memory files (status, bytes, 3-line preview) — helps LLM decide whether to read |
opengrok_read_memory | Read active-task.md or investigation-log.md from the Living Document memory bank |
opengrok_update_memory | Write or append to memory files; auto-timestamps investigation-log.md entries |
🧬 Code Mode (v5+) — For Large Multi-Language Codebases
Set OPENGROK_CODE_MODE=true to switch to a 5-tool interface optimised for multi-step investigations:
| Tool | Purpose |
|---|---|
opengrok_api | Get the full API spec (call once at session start). With OPENGROK_ENABLE_ELICITATION=true, also prompts the user to select a working project if none is configured. |
opengrok_execute | Run JavaScript in a sandboxed QuickJS VM with access to all OpenGrok operations via env.opengrok.* |
All env.opengrok.* calls appear synchronous inside your code — the sandbox bridges async HTTP calls transparently using a SharedArrayBuffer + Atomics channel. Token savings of 80–95% are typical for complex investigations.
v9.0+ sandbox methods for interactive prompts and AI assistance:
| Method | Purpose |
|---|---|
env.opengrok.elicit(message, schema) | Pause execution and ask the user to select from a list — e.g., pick the correct file from multiple matches. Returns { action, content }. Requires OPENGROK_ENABLE_ELICITATION=true. |
env.opengrok.sample(prompt, opts?) | Request an AI-generated string from the client's LLM — e.g., reformulate a zero-result query. Returns string | null (null when client doesn't support sampling). Always null-guard the result. |
When env.opengrok.search() returns zero results and sampling is available, _suggestions: string[] is automatically injected into the result — check it before calling sample() explicitly.
// Example opengrok_execute code
const refs = env.opengrok.search("handleCrash", { searchType: "refs", maxResults: 5 });
const first = refs.results[0];
const content = env.opengrok.getFileContent(first.project, first.path, {
startLine: first.matches[0].lineNumber - 5,
endLine: first.matches[0].lineNumber + 10,
});
return { callerFile: first.path, code: content.content };
The sandbox exposes a Living Document Memory Bank — two persistent markdown files that survive across turns:
| File | Size Limit | Purpose |
|---|---|---|
active-task.md | ≤ 4 KB | Current task state: task:, last_symbol:, next_step:, open_questions:, status: |
investigation-log.md | ≤ 32 KB | Append-only log of findings, grouped by ## YYYY-MM-DD HH:MM: headings |
Access via env.opengrok.readMemory(filename) / env.opengrok.writeMemory(filename, content) inside the sandbox, or via the opengrok_read_memory / opengrok_update_memory / opengrok_memory_status tools in classic mode. Delta encoding returns [unchanged] on repeated reads; richness-scored trimming keeps the most valuable log entries when space is tight.
⚙️ Automated Compilation Data (Optional)
| Tool Name | Capability |
|---|---|
opengrok_get_compile_info | Reads your local compile_commands.json to extract compiler flags, defines, and include directories for exact C/C++ accuracy. |
Project Picker & Interactive Disambiguation (Elicitation)
When OPENGROK_ENABLE_ELICITATION=true, the server uses MCP Elicitation in two places:
- Session start —
opengrok_api(Code Mode) prompts the user to select a working project if noOPENGROK_DEFAULT_PROJECTis configured and more than one project exists. - Mid-execution — Sandbox JS can call
env.opengrok.elicit(message, schema)to ask the user to choose between multiple matching files, revisions, or projects at any point during execution.
Requires a client that supports MCP Elicitation:
- Claude Code v2.1.76+ ✓
Enable in the VS Code configuration panel, or set OPENGROK_ENABLE_ELICITATION=true in your MCP client environment config. The server degrades gracefully to { action: "cancel" } on unsupported clients — no errors.
LLM Sampling
The server delegates LLM calls back to the client via MCP Sampling — using the client's model subscription without needing separate API keys. Used in three places:
- Sandbox error explanation — When
opengrok_executecode fails, sampling generates a concise explanation and fix suggestion. - Dependency graph summarization — Large
opengrok_dependency_mapgraphs (>10 nodes) are summarized via sampling in legacy mode. - Zero-result query reformulation (v9.0+, Code Mode) — When
env.opengrok.search()returns 0 results, sampling auto-injects_suggestionsinto the result object. Sandbox JS can also callenv.opengrok.sample(prompt)explicitly for any AI-generated text.
Supported clients:
- VS Code Copilot ✓
- Claude Code — support pending (tracked in anthropics/claude-code#1785)
The server degrades gracefully when sampling is unavailable — sample() returns null, _suggestions is not injected.
VS Code Integration
Palette Commands
| Command Prompt | Action Performed |
|---|---|
OpenGrok: Manage Configuration | Launches the interactive settings GUI |
OpenGrok: Configure Credentials | Fast CLI-style input for authentication |
OpenGrok: Test Connection | Validates API access and token validity |
OpenGrok: Show Server Logs | Exposes background process stdout/stderr |
OpenGrok: Check for Updates | Polls GitHub for new releases |
OpenGrok: Status Menu | Opens the context menu directly |
Core Settings Profile
Expand for JSON Settings Reference
| Key | Format | Primary Usage |
|---|---|---|
opengrok-mcp.baseUrl | string | The URI of your OpenGrok deployment |
opengrok-mcp.username | string | Authentication identity |
opengrok-mcp.verifySsl | boolean | Disable when using corporate self-signed certs (default: false) |
opengrok-mcp.proxy | string | Optional HTTP traffic router |
Advanced Configuration (v7 — env vars)
For the standalone server (npx opengrok-mcp-server or Claude Code), set these environment variables:
Core Settings
| Variable | Values | Description |
|---|---|---|
OPENGROK_BASE_URL | URL | OpenGrok server base URL (required) |
OPENGROK_USERNAME | string | Authentication username (optional — leave unset for anonymous access) |
OPENGROK_PASSWORD | string | Authentication password (prefer OS keychain via npx opengrok-mcp-server setup) |
OPENGROK_VERIFY_SSL | true (default) / false | Disable TLS verification for self-signed certs |
OPENGROK_TIMEOUT | integer (seconds, default: 30) | HTTP request timeout |
Code Mode & Performance
| Variable | Values | Description |
|---|---|---|
OPENGROK_CODE_MODE | true (default) / false | Switch to 5-tool Code Mode (opengrok_api + opengrok_execute + 3 memory tools) |
OPENGROK_CONTEXT_BUDGET | standard (default) / minimal / generous | Response size tier: 8 KB / 4 KB / 16 KB |
OPENGROK_RESPONSE_FORMAT_OVERRIDE | tsv / toon / yaml / text / markdown | Force a response format globally for all tools |
OPENGROK_DEFAULT_PROJECT | string | Default project name to scope all searches |
OPENGROK_DEFAULT_MAX_RESULTS | integer (default: 25) | Default search result limit |
OPENGROK_LOCAL_COMPILE_DB_PATHS | comma-separated paths | Paths to compile_commands.json for C/C++ compiler flag extraction |
OPENGROK_ENABLE_CACHE_HINTS | true / false (default: false) | Enable cache-control: immutable hints for prompt caching infrastructure |
Memory Bank
| Variable | Values | Description |
|---|---|---|
OPENGROK_MEMORY_BANK_DIR | path | Override directory for active-task.md + investigation-log.md files |
OPENGROK_ENABLE_OBSERVATION_MASKER | true / false (default: false) | Prepend compact history summaries to opengrok_execute results after the full-text window fills. Only useful for clients that truncate context (not Claude Code or Cursor). |
OPENGROK_OBSERVATION_MASKER_TURNS | integer (default: 10) | Full-text window size: how many of the most-recent opengrok_execute results to keep in full before older ones are replaced with compact summaries. |
Rate Limiting
| Variable | Values | Description |
|---|---|---|
OPENGROK_RATELIMIT_ENABLED | true (default) / false | Enable token-bucket rate limiting |
OPENGROK_RATELIMIT_RPM | integer (default: 60) | Global requests-per-minute limit |
OPENGROK_PER_TOOL_RATELIMIT | tool:rpm,tool:rpm | Per-tool RPM overrides (e.g., opengrok_execute:10,opengrok_batch_search:20) |
Response Cache
| Variable | Values | Description |
|---|---|---|
OPENGROK_CACHE_ENABLED | true (default) / false | Enable TTL response cache |
OPENGROK_CACHE_MAX_SIZE | integer (default: 500) | Max cache entries |
OPENGROK_CACHE_SEARCH_TTL | seconds (default: 300) | Search result cache TTL |
OPENGROK_CACHE_FILE_TTL | seconds (default: 600) | File content cache TTL |
OPENGROK_CACHE_HISTORY_TTL | seconds (default: 1800) | File history cache TTL |
OPENGROK_CACHE_PROJECTS_TTL | seconds (default: 3600) | Project list cache TTL |
Security & Audit
| Variable | Values | Description |
|---|---|---|
OPENGROK_AUDIT_LOG_FILE | path | File path for structured audit log (CSV or JSON) |
MCP Protocol Features
| Variable | Values | Description |
|---|---|---|
OPENGROK_ENABLE_ELICITATION | true / false (default: false) | Enable project picker at opengrok_api startup (Code Mode) and env.opengrok.elicit() in sandbox. Requires a supporting MCP client. |
OPENGROK_ENABLE_FILES_API | true / false (default: false) | Enable FileReferenceCache for investigation-log.md (SHA-256 content-addressed) |
OPENGROK_SAMPLING_MODEL | string | Model preference for MCP Sampling (error explanation, graph summarization) |
OPENGROK_SAMPLING_MAX_TOKENS | integer (default: 256, max: 4096) | Token budget for MCP Sampling responses |
OpenGrok API
| Variable | Values | Description |
|---|---|---|
OPENGROK_API_VERSION | v1 (default) / v2 | OpenGrok REST API version (v2 required for opengrok_call_graph) |
HTTP Transport (v7.0+)
| Variable | Values | Description |
|---|---|---|
OPENGROK_HTTP_PORT | integer | Expose Streamable HTTP transport on this port (in addition to stdio) |
OPENGROK_HTTP_MAX_SESSIONS | integer (default: 100) | Max concurrent HTTP sessions before new connections are rejected |
OPENGROK_HTTP_AUTH_TOKEN | string | Static Bearer token for HTTP endpoint authentication |
OPENGROK_JWKS_URI | URL | JWKS endpoint for JWT validation (OAuth 2.1 resource server mode) |
OPENGROK_RESOURCE_URI | URL | This server's resource URI, advertised in RFC 9728 metadata |
OPENGROK_AUTH_SERVERS | comma-separated URLs | Trusted authorization server URIs |
OPENGROK_SCOPE_MAP | scope:role,... | Map JWT scopes to RBAC roles (e.g., read:readonly,admin:admin) |
OPENGROK_STRICT_OAUTH | true / false | Reject requests without a valid JWT when OPENGROK_JWKS_URI is set |
OPENGROK_ALLOWED_ORIGINS | comma-separated origins | CORS allowlist (replaces wildcard CORS) |
OPENGROK_RBAC_TOKENS | tok1:role,tok2:role | Role-based access tokens: admin / developer / readonly |
Logging
| Variable | Values | Description |
|---|---|---|
OPENGROK_LOG_LEVEL | debug / info (default) | Verbose structured logging to stderr |
VS Code users can set opengrok-mcp.codeMode, opengrok-mcp.contextBudget, opengrok-mcp.memoryBankDir, opengrok-mcp.defaultProject, opengrok-mcp.responseFormatOverride, opengrok-mcp.compileDbPaths, opengrok-mcp.enableObservationMasker, and opengrok-mcp.observationMaskerTurns in VS Code settings instead.
MCP SDK Note: This version uses
@modelcontextprotocol/sdkv1.29.0. MCP SDK v2 is in pre-alpha; we will migrate when stable (expected Q3-Q4 2026). v2 will enable enhanced completions for tool parameters and resource templates.
HTTP Transport (v7.0+)
By default the server communicates over stdio (standard MCP). For team deployments, you can also expose a Streamable HTTP endpoint:
OPENGROK_HTTP_PORT=3666 npm run serve
# or add to your MCP client config:
# "OPENGROK_HTTP_PORT": "3666"
Session Management
- Each HTTP client receives an isolated
McpServerinstance (per-session factory pattern) - Sessions expire after 30 minutes of inactivity;
OPENGROK_HTTP_MAX_SESSIONScaps concurrent sessions (default: 100) GET /mcp/sessionsreturns JSON with active session count and oldest session age
Authentication
Configure one of the following:
| Method | Config |
|---|---|
| Static Bearer token | OPENGROK_HTTP_AUTH_TOKEN=mysecret |
| OAuth 2.1 resource server | OPENGROK_JWKS_URI=https://idp.example.com/.well-known/jwks.json + OPENGROK_RESOURCE_URI=https://opengrok-mcp.example.com |
| RBAC with named roles | OPENGROK_RBAC_TOKENS='alice-token:admin,bot-token:readonly' |
In resource server mode, this server validates JWTs issued by your own IdP — there is no built-in /token endpoint. RFC 9728 protected resource metadata is served at /.well-known/oauth-protected-resource.
RBAC Roles
| Role | Permissions |
|---|---|
admin | Full access to all tools and configuration |
developer | All search, read, memory, and code tools |
readonly | Search and read tools only; no memory writes, no code execution |
Fail-safe: unknown or missing tokens default to
readonly, notadmin.
Security (v7.0+)
v7.0 includes a comprehensive security audit with the following hardening:
| Area | Protection |
|---|---|
| SSRF | DNS rebinding detection + IPv6-mapped address blocking in buildSafeUrl |
| Path traversal | NFC normalization + bidirectional Unicode character blocking |
| HTML injection | he.decode on all parser text nodes before display |
| Prompt injection | escapeMarkdownField in all formatters |
| Token comparison | crypto.timingSafeEqual for all Bearer token comparisons |
| CORS | Allowlist via OPENGROK_ALLOWED_ORIGINS (no wildcard in production) |
| Security headers | X-Content-Type-Options, X-Frame-Options, CSP on HTTP responses |
| Credential encryption | AES-256-GCM (migrated from CBC; auto-upgrades existing files) |
| Rate limiting | Integer-based token bucket (eliminates float drift) |
| ReDoS | minimatch for glob patterns |
| Audit logs | Injection-escaped structured audit entries |
⚠️ v7.0.0 Breaking Changes
OPENGROK_HTTP_CLIENT_IDandOPENGROK_HTTP_CLIENT_SECRETremoved. Migrate toOPENGROK_JWKS_URI+OPENGROK_RESOURCE_URIfor OAuth 2.1 (resource server model — bring your own IdP).- Memory bank
migrate()removed — the legacy 6-file layout is no longer supported. The 2-file layout (active-task.md+investigation-log.md) has been the default since v5.4.- CORS is now allowlist-only when
OPENGROK_ALLOWED_ORIGINSis set; unauthenticated wildcard CORS is disabled.
System Architecture
Show topological diagram
[ AI Client ] [ Integration Layer ] [ Data Source ]
│ │
+---------------+ │ +-------------------+ │ +----------------------+
│ GitHub │<──(stdio)──┼──────>│ OpenGrok MCP │<────┼─────>│ OpenGrok REST API & │
│ Copilot Chat │ │ │ Server (Node.js) │HTTP │ │ Web Interface │
+---------------+ │ +-------------------+ │ +----------------------+
│ ▲ │ │
│ │ (Configures & Hosts) │ (Context Optimization)
▼ │ │ │
+---------------+ │ o Context Fetch │ +----------------------+
│ VS Code │ │ o Multi-Search │ │ Local File System │
│ Extension │ │ o Auto-Truncate │<─────┤ (compile_commands) │
+---------------+ │ │ +----------------------+
The underlying code is completely packaged in the marketplace extension via esbuild. The server uses standard VS Code Node APIs without external VM requirements.
Building & Testing
# Initializing
npm install
# Code Quality & Tests
npm run lint # Strict TypeScript & ESLint validation
npm test # Execute the Vitest test suite (1113 tests)
npm run test:sandbox # Sandbox integration tests (requires compile first)
npm run test:coverage # Coverage report (≥89% threshold)
# Packaging
npm run compile # Generate the esbuild artifact (includes sandbox-worker.js)
npm run vsix # Create the downloadable extension file
We leverage GitHub Actions for automated CD. Tagging a commit (e.g., v1.2.3) automatically triggers the build matrix and attaches artifacts to a new GitHub Release.
For deep-dives into the architecture or PR guidelines, please read CONTRIBUTING.md.
Troubleshooting & Support
The MCP tools are missing in Copilot Chat
- Click the paperclip (
🔧) icon to "Update Tools" - Run
Developer: Reload Window
"Connection failed" errors
- Double-check your
OPENGROK_BASE_URL - Make sure you aren't blocked by corporate VPNs/proxies
401 Unauthorized / Authentication failing
- Run the
OpenGrok: Configure Credentialscommand to save your username/password again
Self-Signed SSL Certificates
- Turn off strict validation by setting
opengrok-mcp.verifySsltofalse
Slow queries or timeouts
- Limit the scope using the
file_typeargument or targeting a specific project - OpenGrok might be indexing; run
opengrok_index_health
Need verbose logs?
- Set the environment variable
OPENGROK_LOG_LEVEL=debugto get extensive stdout trace data
OpenGrok Version Compatibility
| OpenGrok Engine | Status | known limitations |
|---|---|---|
| v1.13.x and above | Native Support | None (Full REST API functionality) |
| v1.7.0 — v1.12.x | Legacy Mode | Uses HTML scraping for symbol lookups and blame |
| Below v1.7.0 | Unsupported | Unpredictable behaviour |
License Information
This system is distributed under the PolyForm Noncommercial License 1.0.0.
- ✅ Permitted: Personal use, hobby projects, academic research, education
- ❌ Prohibited: Any commercial, business, enterprise, or paid utilization
Commercial Licensing: To use this extension in an enterprise context (internal tooling, CI pipelines, business infrastructure), a commercial license is strictly required. Reach out to rudroy09@gmail.com for enterprise tier pricing.
Read LICENSE-COMMERCIAL.md for full terms.