Lint JavaScript/TypeScript files with ESLint rules and get structured diagnostics via @eslint/mcp (npx) — official ESLint MCP server

@eslint/mcp v0.3.8 — Official ESLint MCP Server

Package: @eslint/mcp (npm, official from ESLint team) Author: Nicholas C. Zakas (ESLint creator) Transport: stdio Dependencies: @modelcontextprotocol/sdk, eslint, zod Credential-free: yes Requires: eslint.config.js (flat config) in the project being linted

Tools (1)

Response Structure

The response has 2+N content items (N = number of files with results):

• content[0]: Instruction text: 'Here are the results...display the full list to the user'
• content[1..N]: One JSON string per file with: filePath, messages[] (each with ruleId, severity 1=warn/2=error, message, line, column, endLine, endColumn, messageId, suggestions[]), errorCount, warningCount, fixableErrorCount, source (original file content)
• content[last]: Instruction about whether to auto-fix

Key Observations

1. Requires flat config (ESLint 9+) — must have eslint.config.js in the project tree. Without it: 'Could not find config file.' Old .eslintrc format not supported.
2. Server cwd matters — the server prints 'ESLint MCP server is running. cwd: ...' and resolves configs from there. The filePaths must be absolute.
3. `console` flagged as `no-undef` — with @eslint/js recommended config, console is not defined (no globals for browser/node). Clean files still get errors unless globals are configured.
4. Detects real issues — no-unused-vars, no-unreachable, no-undef all triggered correctly on test files. Suggestions include fix ranges for auto-repair.
5. Multi-file support — pass multiple absolute paths; each file gets its own JSON diagnostics object in a separate content item.
6. First lint is slowest (~900ms config loading + parsing), subsequent files ~180-360ms.
7. Nonexistent files — returns a clear error: 'No files matching ... were found.' (not an exception).

Gotchas

• Only 1 tool — no format, fix, or config inspection tools. Just lint-files.
• Absolute paths required — relative paths are resolved from server cwd, which may not be your project.
• ESLint deprecation warnings — the unstable_config_lookup_from_file flag warning appears on stderr; harmless but noisy.
• Response includes LLM instructions — the preamble and footer tell the LLM to 'display results to user' and 'ask before fixing'. These are part of the content, not metadata.
• No streaming — all files linted synchronously, results returned at once.