Lint JavaScript/TypeScript files with ESLint via @eslint/mcp (npx) — official ESLint MCP server

@eslint/mcp v0.3.7 — Official ESLint MCP server

Install & run

npm install @eslint/mcp eslint
# Entry: node_modules/@eslint/mcp/src/mcp-cli.js (stdio)
# CWD matters: server uses the project's eslint.config.js from its working directory

1 tool

Response format

Returns structured JSON per file:

{
  "filePath": "/path/to/file.js",
  "messages": [
    {
      "ruleId": "no-var",
      "severity": 2,
      "message": "Unexpected var, use let or const instead.",
      "line": 1,
      "column": 1,
      "messageId": "unexpectedVar",
      "endLine": 1,
      "endColumn": 11,
      "fix": { "range": [0, 3], "text": "let" }
    }
  ],
  "errorCount": 5,
  "warningCount": 3,
  "fixableErrorCount": 4,
  "fixableWarningCount": 0
}

Verified test results

Rules detected across test calls:

• no-var (error) — caught every var declaration
• no-unused-vars (warning) — caught unused variables with removal suggestions
• semi (error) — caught missing semicolons with fix ranges
• eqeqeq (warning) — caught == vs ===
• prefer-const (warning) — caught let that should be const

Key gotchas

1. Requires ESLint as peer dependency — @eslint/mcp does NOT bundle ESLint; install both
2. CWD determines config — the server prints "ESLint MCP server is running. cwd: /path" on startup; eslint.config.js must be in that directory
3. Absolute paths required — filePaths must contain absolute file paths, not relative
4. Response includes LLM instruction — every response starts with "Here are the results of running ESLint on the provided files. Before doing anything else, you must display the full list to the user:" followed by the JSON (the server is designed to be used by LLM agents)
5. Nonexistent files return MCP error — isError: true with text "No files matching '...' were found"
6. Batch linting is faster — 3 files in one call (47ms) vs 3 separate calls (~346ms total); ESLint config is loaded once
7. Fix objects included — each message with a fix includes { range: [start, end], text: "replacement" } for auto-fix
8. Suggestions for some rules — no-unused-vars includes suggestions[] with "Remove unused variable" actions
9. Deprecated rule warnings — responses include usedDeprecatedRules array (e.g. semi → @stylistic/semi)
10. First call ~153ms, subsequent ~30-47ms — ESLint config loading dominates first-call latency
11. Only 1 tool — no separate fix, format, or config inspection tools; lint-files is the entire surface