OnlineCompiler.io

Name: OnlineCompiler.io
Author: onlinecompiler-io

by onlinecompiler-ioversion 1.2.1i★ –iRuns in the cloud

Registry nameio.onlinecompiler/compiler

Install

Overview

Description from the maker (original English)

Run Python, Java, C, C++, C#, Go, Rust and 39 more languages, each run in a fresh, offline sandbox.

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi3 of 3 passedChecked from public information; code not scanned yet
UsageiEarly★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Runs in the cloud
Transport: Streamable HTTP
Category: Developer tools
You need to fill in: Authorization

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 3 of 3 passed
Runs on the maker’s server: what you ask it goes through their server.
You fill in yourself: Authorization

Values marked secret are keys to your account. Never share them or paste them into a chat.

You need

Runs in the cloudNothing to install; it connects over the internet

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

This address needs a key in a request header, which the add-connector menu cannot set. Use Claude Code, Cursor or VS Code instead.

Run this in your terminal

claude mcp add --transport http compiler https://api.onlinecompiler.io/mcp --header 'Authorization: Bearer {api_key}'

Fill in the empty values before running it.

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "compiler": {
      "url": "https://api.onlinecompiler.io/mcp",
      "headers": {
        "Authorization": "Bearer {api_key}"
      }
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "compiler": {
      "type": "http",
      "url": "https://api.onlinecompiler.io/mcp",
      "headers": {
        "Authorization": "Bearer {api_key}"
      }
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

This address needs a key in a request header, which the add-connector menu cannot set. Use Claude Code, Cursor or VS Code instead.

Your choice stays on this device in a cookie; no account needed.

Values you fill in

Authorization secret HTTP header
Optional: your OnlineCompiler.io API key as a Bearer token. Leave it out to sign in with OAuth instead. Get a free key at https://api.onlinecompiler.io/compilers/api-keys/

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

The server asks you to sign in before it lists its tools.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 8, 2026

✓ Pass
Maker matches the repo
The registry name was verified against the domain onlinecompiler.io (the registry checks domain ownership)
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
✓ Pass
Endpoint responds
Responded in 207 ms (HTTP 401)
✓ Pass
Sign-in with OAuth
Declares OAuth sign-in, so your AI app can take you to log in
… Not checked yet
No hidden instructions in tool descriptions
Not checked yet; we read the tool list when we check the endpoint

Compared with others in Developer toolsi

More stars than 0% of the other 4930 servers in this category
Published to the registry more recently than 97% of the other 4930 servers in this category
Basic checks equal to or better than 100% of the other 4930 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is OnlineCompiler.io safe?

It passed 3 of 3 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

You need to fill in: Authorization

Does it run on my computer or in the cloud?

It runs in the maker’s cloud. Connect over the internet with nothing to install, but what you send passes through the maker’s servers.

Is it still maintained?

The GitHub repo last changed –, and the latest version (1.2.1) reached the registry yesterday.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. It connects by URL, so apps that accept remote MCP servers work too, such as ChatGPT in developer mode.

What can I use instead?

In the same category: GitHub, Desktop Commander, Cloudflare MCP

Alternatives

Servers in the same category from other makers, sorted by stars.

Reading a card:↓ Downloads per weeki★ GitHub starsiThree pillars: reviews · checks · usageiUpdated = latest version published to the registryi

GitHub

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Cloudflare MCP

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Runs in the cloud✓ mcp.cloudflare.com

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README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

OnlineCompiler MCP Server

An MCP server that lets AI assistants execute code in 46 programming languages via OnlineCompiler.io.

Each run starts a fresh gVisor sandbox (512 MB RAM, 30 s timeout, no network access).

Supported Languages

Python, C, C++, Fortran, Java, C#, F#, Visual Basic, Go, Rust, PHP, Ruby, Haskell, TypeScript (Deno), JavaScript (Node.js), Kotlin, R, Bash, SQL (SQLite), SQL (DuckDB), Swift, COBOL, Perl, Julia, Pascal, Octave, Assembly (NASM), Lua, OCaml, Common Lisp, Erlang, Elixir, Prolog, D, FreeBASIC, Dart, Clojure, Groovy, Scala, Zig, Nim, Crystal, Ada, PowerShell, Racket and Objective-C. list_compilers returns the current list with versions.

Setup

Point your MCP client at the URL. No install needed.

https://api.onlinecompiler.io/mcp

There are two ways in:

Sign in (OAuth). Clients that support MCP sign-in (claude.ai, Claude Desktop and mobile, ChatGPT, Claude Code, Codex) open an OnlineCompiler.io sign-in page (Google or an email link) and ask you to approve. The app then appears as a key named after it, for example "Claude (connected app)", on your API Keys page. Disable that key to disconnect the app.
API key. Send your key as Authorization: Bearer (the bare key works too). Get a free key on the API Keys page.

Runs count against your plan either way. A wrong or disabled key gets 401.

Tools

`list_compilers`

List all available compilers with their identifiers.

`run_code`

Execute code with a specified compiler.

Parameters:

code (required): Source code to execute
compiler (required): Compiler identifier from list_compilers (e.g. python-3.14, gcc-15)
input (optional): Standard input for the program
time_limit (optional): Seconds the run may take, above 0 and at most 30 (default 30)
files (optional): Files the program can use, up to 20 and 1,000,000 decoded bytes in total: helper source files (compiled with the program) and input data. Each {"name": "util.py" or "pkg/util.py", "content": "...", "encoding": "utf8" or "base64"}; the program finds them in its working directory

python-3.14 includes numpy, pandas, scipy, scikit-learn, matplotlib, seaborn, statsmodels, sympy, openpyxl, pillow and duckdb. Files a program writes to $OUTPUT_DIR come back (png, svg, csv, json, txt; up to 8 files and 2 MB), and plt.show() saves each open figure as a PNG.

Returns: output, error, status, exit_code, time, memory, truncated, files, files_truncated. PNG files arrive as MCP image content; SVG, CSV, JSON and text files are listed with their text (cut at 64 KB).

`run_tests`

Check a program against test cases and judge it like an online judge. At most 10 tests per call, each counting as one run. Every test runs unless the code fails to compile or the request runs out of time.

Parameters:

code (required): Source code to check
compiler (required): Compiler identifier from list_compilers
tests (required): Up to 10 objects, each {"input": "...", "expected_output": "..."}
time_limit (optional): Seconds per test, above 0 and at most 30 (default 2); compiling does not count, and Java, Groovy and F# get a start-up allowance on top
checker (optional): trim (default), exact, tokens, float or rows (unordered lines, numbers within tolerance)
files (optional): Files shared by every test (input data or helper source files), same shape as in run_code

Returns: an overall verdict, a score from 0 to 100 and a verdict per test.

`judge_problem`

Judge code against one of your stored problems. Hidden tests return only their verdict, never their input or expected output. Nothing is invented: a missing problem or a failed run is an error (for example HTTP 404: Problem not found).

Parameters:

problem (required): The id or slug of one of your stored problems
compiler (required): Compiler identifier from list_compilers
code (required): Source code to judge
mode (optional): all (default) runs every test; samples runs only the sample tests

Returns: a verdict, a score, a per-test verdict, a summary, a submission id, a signed receipt, and the problem id and version.

Client Configuration

claude.ai, Claude Desktop and mobile

In claude.ai or Claude Desktop, open Customize, then Connectors, then Add custom connector. Paste https://api.onlinecompiler.io/mcp, sign in to OnlineCompiler.io when asked and approve. The connector belongs to your Claude account, so it works in the Claude mobile apps too.

ChatGPT

Turn on developer mode in ChatGPT's settings, add a custom connector with https://api.onlinecompiler.io/mcp and sign in when asked.

Claude Code

claude mcp add --transport http onlinecompiler https://api.onlinecompiler.io/mcp

Then run /mcp inside Claude Code, pick onlinecompiler and sign in. To use an API key instead:

claude mcp add onlinecompiler https://api.onlinecompiler.io/mcp --transport http --header "Authorization: Bearer YOUR_API_KEY"

Gemini CLI

Install the extension from this repository:

gemini extensions install https://github.com/onlinecompiler-io/onlinecompiler-mcp

It adds the hosted server at https://api.onlinecompiler.io/mcp and a short context file telling Gemini when to use the tools. Gemini CLI signs you in with OAuth. To use an API key instead, add the server by hand in ~/.gemini/settings.json:

"mcpServers": { "onlinecompiler": { "httpUrl": "https://api.onlinecompiler.io/mcp", "headers": { "Authorization": "Bearer your-api-key" } } } }

Claude Code plugin

This repository is also a Claude Code plugin marketplace:

/plugin marketplace add onlinecompiler-io/onlinecompiler-mcp

/plugin install onlinecompiler@onlinecompiler

Then run /mcp, pick onlinecompiler and sign in. The plugin does the same as the claude mcp add command above.

Cline

See llms-install.md: add the URL as a remote server with your API key in an Authorization header.

Codex

codex mcp add onlinecompiler --url https://api.onlinecompiler.io/mcp

codex mcp login onlinecompiler

To use an API key instead, skip the login and put the key in the environment variable that bearer_token_env_var names, in ~/.codex/config.toml:

[mcp_servers.onlinecompiler]

url = "https://api.onlinecompiler.io/mcp" bearer_token_env_var = "ONLINECOMPILER_API_KEY"

VS Code (Copilot / Claude extension)

Add to .vscode/mcp.json:

"servers": { "onlinecompiler": { "url": "https://api.onlinecompiler.io/mcp", "headers": { "Authorization": "Bearer your-api-key" } } } }

Cursor

Add to .cursor/mcp.json:

"mcpServers": { "onlinecompiler": { "url": "https://api.onlinecompiler.io/mcp", "headers": { "Authorization": "Bearer your-api-key" } } } }

OnlineCompiler.io

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

Values you fill in

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Developer toolsi

Common questions

Alternatives

GitHub

Desktop Commander

Cloudflare MCP

README from the maker

OnlineCompiler MCP Server

Supported Languages

Setup

Tools

list_compilers

run_code

run_tests

judge_problem

Client Configuration

claude.ai, Claude Desktop and mobile

ChatGPT

Claude Code

Gemini CLI

Claude Code plugin

Cline

Codex

VS Code (Copilot / Claude extension)

Cursor

`list_compilers`

`run_code`

`run_tests`

`judge_problem`