drawio-mcp-server AGENTS.md

Draw.io MCP Server

Logging discipline (drawio-mcp-server)

When the stdio transport is active, stdout must contain only JSON-RPC frames produced by the MCP SDK. A single stray console.log will cause spec-strict clients (e.g. codex-cli) to reject the server. The rules below codify this.

1. Stdout discipline. console.log, console.info, console.dir, and process.stdout.write are banned in packages/drawio-mcp-server/src/** outside the allowlist below. The MCP SDK transport is the only legitimate writer to stdout.
2. Logger usage. Every production function that needs to emit a diagnostic MUST receive an AppLogger (index.ts) or Logger (types.ts) — as a parameter or via Context.log. Constructing a logger inside a function is forbidden except in the entry-point files listed in rule 3.
3. Allowlist (the only files permitted to call console.*):
   • src/mcp_console_logger.ts — the stderr bridge implementation.
   • src/mcp_server_logger.ts — internal console.error for unrecoverable invalid-level guard.
   • src/standard_console_logger.ts — test-only logger (writes to stdout). Do not import from production code.
   • src/index.ts — only via the module-scope fatalLog constant. No other site in index.ts may use console.*.
   • src/prefetch-assets.ts — separate CLI entrypoint; instantiates mcp_console_logger and uses it.
   • src/**/*.test.ts — tests may use console and standard_console_logger freely.
4. Pre-boot phase. Code that runs before createDrawioMcpApp({ config }) returns (CLI help, config-parse failure) uses fatalLog. After the app exists, use app.log or a logger provided by dependency injection.
5. Two logger modes. --logger console (default) writes to stderr; --logger mcp-server sends MCP notifications/message to the connected client. No other logging output channels exist; do not add raw process.stderr.write either — go through the logger.
6. Transport-mode awareness. src/stdio-transport-purity.test.ts spawns the binary with --transport stdio and asserts every non-empty stdout line parses as JSON. This catches stdout contamination introduced by future commits.
7. Browser packages exempt. packages/drawio-mcp-extension/** and packages/drawio-mcp-plugin/** execute in a browser context and may use console.* freely; they share no streams with the MCP server.
8. Lint enforcement (Biome). biome check src/ runs as part of pnpm --filter drawio-mcp-server lint and enforces noConsole for src/** with the per-file overrides matching rule 3. Biome is a devDep of drawio-mcp-server and pinned via the pnpm catalog.