Run code snippets in 35 languages (JS, Python, Go, Ruby, etc.) via mcp-server-code-runner (npx)

Recipe: Run code snippets in 35 languages via mcp-server-code-runner (npx)

Server: [email protected] · npm · stdio Launch: npx -y mcp-server-code-runner Auth: none Tools (1):

• run-code — accepts code (string) and languageId (enum of 35 languages), writes to a temp file, executes with the system's installed runtime, returns stdout.

Supported languages (35): javascript, typescript, python, ruby, go, rust, php, perl, perl6, lua, groovy, powershell, bat, shellscript, fsharp, csharp, vbscript, coffeescript, scala, swift, julia, crystal, ocaml, r, applescript, clojure, racket, scheme, ahk, autoit, dart, haskell, nim, lisp, kit, v, sass, scss

Prerequisite: The target language's runtime must be installed on the host machine (e.g. node for JavaScript, python3 for Python, go for Go).

Trace: JavaScript — compute first 10 primes and their sum

// REQUEST
{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"run-code","arguments":{"code":"const primes = []; for (let n = 2; primes.length < 10; n++) { if ([...Array(n).keys()].slice(2).every(i => n % i)) primes.push(n); } console.log(\"First 10 primes:\", primes); console.log(\"Sum:\", primes.reduce((a,b) => a+b, 0));","languageId":"javascript"}}}

// RESPONSE
{"result":{"content":[{"type":"text","text":"First 10 primes: [\n   2,  3,  5,  7, 11,\n  13, 17, 19, 23, 29\n]\nSum: 129\n"}]},"jsonrpc":"2.0","id":2}

How it works internally

1. Writes code to a temp file (e.g. /tmp/tmp.js)
2. Executes via the language's CLI (e.g. node "/tmp/tmp.js")
3. Returns stdout as a text content block

Notes

• Server logs execution commands to stdout (before the JSON-RPC response), e.g. Temporary file created at: /tmp/tmp.js and Executing command: node "/tmp/tmp.js" — these are informational, not part of the MCP response.
• No sandboxing — code runs with the same permissions as the npx process. For untrusted code, run inside a container.
• Execution time depends on the snippet and runtime startup; JavaScript is near-instant, compiled languages (Go, Rust) include compile time.
• Python execution may need extra wait time due to runtime startup.
• The server supports tools.listChanged capability, suggesting it can dynamically update its tool list.