OpenGrok MCP Server

31 tools total: 2–5 in Code Mode (opengrok_api + opengrok_execute, plus 3 memory tools when OPENGROK_ENABLE_MEMORY_TOOLS=true) and 26 in standard mode (OPENGROK_CODE_MODE=false).

Primary Tools

Compound Tools

These merge multiple API calls into a single operation.

Investigation Tools

(Note: search tools support language filtering. Pass file_type using the canonical analyzer name — cxx for C++, golang for Go, sh for shell, javascript for JS. Aliases accepted: cpp/c++→cxx, go→golang, bash/shell→sh, js→javascript, ts→typescript, cs→csharp, py→python, rb→ruby, rs→rust.)

defs/refs/symbol fallback notes — defs, refs, and symbol searches require a project scope (pass projects or set OPENGROK_DEFAULT_PROJECT); without one they may return too many cross-project hits. On instances where the REST endpoint returns an error or empty results for these types, the client automatically falls back to web-UI parsing so the LLM still gets answers. opengrok_call_graph needs API v2 and degrades to a refs-based view on v1.

Set OPENGROK_CODE_MODE=true (the default). Call opengrok_api once at session start to receive the full API spec. All subsequent operations go through opengrok_execute.

All sandbox API calls are synchronous — flat globals (search(...)), no await. The env.opengrok.* object form (env.opengrok.search(...)) is equivalent.

Search & Discovery

search() uses canonical file type names only (e.g. cxx, golang, sh) — see the alias list above. Pass expandFunction: true to expand matching results to their enclosing function body (adds host-side reads, up to 3 files per call).

Cursor pagination — Methods that return a cursor field (search, findFile, browseDir, getFileSymbols, getFileHistory, getFileDiff) support pagination. Pass the cursor back as opts.cursor on the next call to fetch the next page. If a cursor has expired (session restarted or too much time elapsed), the response contains { _cursorExpired: true } — restart pagination from the beginning.

Read & Navigate

History & Blame

Code Intelligence

traceCallChain callers come from refs search; callees come from tree-sitter AST analysis for supported languages (C/C++, Java, Go, Python, JS/TS, Rust, and more). Both long-running methods fan out over a background client — a rate-limit-free sibling connection with a short per-operation budget — so deep traversals don't consume the foreground rate-limit quota.

System

Example

// Example opengrok_execute codeconst 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 };

When search() returns zero results and sampling is enabled, _suggestions: string[] is automatically injected into the result — check it before calling sample() explicitly.

Tree-sitter intelligence — range reads and expandFunction expand matches to enclosing function bodies using tree-sitter AST analysis (WASM grammars, no host toolchain needed). Per-tier line budgets apply: minimal 200 lines, standard 400 lines, generous 600 lines. Override the grammar directory with OPENGROK_GRAMMAR_DIR; contribute new grammars via npm run copy-grammars (see CONTRIBUTING.md).

fitToBuffer truncation — sandbox results that exceed the 8 MB bridge buffer are trimmed by fitToBuffer(), which keeps complete result elements rather than truncating mid-JSON. Trimmed results carry _truncated: true — narrow the query or page with cursor when you see it.

Elicitation (OPENGROK_ENABLE_ELICITATION=false to disable, default: true)

When enabled, opengrok_api prompts the user to select a working project at session start if no OPENGROK_DEFAULT_PROJECT is configured and more than one project exists. Sandbox code can also call env.opengrok.elicit() to ask the user to choose between multiple matches during execution. Requires a client that supports MCP Elicitation — Claude Code v2.1.76+ supports this. Degrades gracefully to { action: "cancel" } on other clients.

Sampling (OPENGROK_ENABLE_SAMPLING=true, default: false)

Delegates LLM calls back to the client via MCP Sampling, using the client's model subscription without separate API keys. Triggers automatically in three places: sandbox error explanation, large dependency graph summarization (>10 nodes), and zero-result query reformulation (_suggestions injection). VS Code Copilot supports sampling; other clients vary. The server degrades gracefully when sampling is unavailable.

[!WARNING] Sampling triggers are automatic — not on-demand. A single investigation session can generate many sampling calls across sandbox errors, zero-result searches, and large dependency graphs. Some clients consume premium requests per call after the first confirmation prompt. Enable with this in mind.

Code Mode includes 2 tools by default (api + execute; 5 with OPENGROK_ENABLE_MEMORY_TOOLS=true). Two files persist across turns and session restarts:

Delta encoding returns [unchanged] on repeated reads of unmodified content. Richness-scored trimming keeps the highest-value log entries when space is tight.

Core

Code Mode & Performance

Memory Bank

Rate Limiting

Response Cache

MCP Protocol

OpenGrok API

Security & Audit

Logging

Proxy

VS Code users can set opengrok-mcp.baseUrl, 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. Secret values such as the password are never written to VS Code settings.

MCP SDK Note: This version uses @modelcontextprotocol/sdk v1.30.0 (v1 line).

By default the server communicates over stdio. For shared team deployments, the HTTP transport layer is available as a library API (startHttpTransport() in src/server/transport/http-transport.ts) but is not yet wired into the CLI entry point — OPENGROK_HTTP_PORT is documented below but main.ts does not yet read it to start the HTTP server automatically. Use startHttpTransport() directly in custom deployments.

Session Management

• Each HTTP client receives an isolated McpServer instance (per-session factory pattern)
• Sessions expire after 30 minutes of inactivity; OPENGROK_HTTP_MAX_SESSIONS caps concurrent sessions (default: 100)
• GET /mcp/sessions returns JSON with active session count and oldest session age

Authentication

In resource server mode, this server validates JWTs issued by your own IdP — there is no built-in /token endpoint. When OPENGROK_JWT_ISSUER is set, tokens from other issuers are rejected. RFC 9728 protected resource metadata is served at /.well-known/oauth-protected-resource.

RBAC Roles

Unknown or missing tokens are rejected with 403 Forbidden. When no authentication is configured, unauthenticated requests are granted admin (local dev mode).

CORS

Browser-based clients are gated by an origin allowlist (OPENGROK_ALLOWED_ORIGINS, comma-separated). Without auth configured, loopback origins (localhost, 127.0.0.1, [::1]) are allowed for local development; once auth is configured (OPENGROK_HTTP_AUTH_TOKEN or RBAC tokens), loopback is no longer implicit — list every allowed origin explicitly, including local ones.

For the full security architecture (threat model, defense layers, hardening guide), see SECURITY.md.

Sandbox trust recommendation: When configuring OpenGrok MCP in VS Code's MCP settings, you may set sandboxEnabled: true which auto-approves tool calls without confirmation prompts. This is safe because all tool execution occurs inside the QuickJS WASM sandbox with no host access — the LLM cannot execute arbitrary system commands through this server.