onlinecompiler-io Reference API
Compilers, limits and health. No API key needed.
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OpenAPI Specification
openapi: 3.2.0
info:
title: OnlineCompiler.io Reference API
version: '2026-10-24'
summary: Run code in a sandbox, judge it against test cases, and read limits and usage.
description: 'Execute source code in isolated, network-less sandboxes in dozens of languages and get stdout, stderr, exit code, time and memory back as JSON. This file describes the native REST API: synchronous runs, asynchronous runs with a callback, judging a program against test cases, the compiler list, execution limits, usage and health.
**Authentication.** Create an API key (type API) in the dashboard at https://api.onlinecompiler.io/compilers/api-keys/ and send the bare key in the `Authorization` header, for example `Authorization: YOUR_API_KEY`. A `Bearer ` prefix is not accepted on this API. Widget keys cannot call it. `GET /api/compilers/`, `GET /api/limits/` and `GET /api/health/` need no key.
Paths are written with a trailing slash; every path except `/api/files/{file_id}/` also works without it.
**Limits.** Per-run limits (memory, CPUs, timeout, output size, file counts) and your plan''s allowance and rate limits change over time and are not repeated here: read `GET /api/limits/` for the defaults and `GET /api/usage/` for your account. A refusal for a limit answers HTTP 429 with `{"error": "..."}` and nothing runs or is counted.
**Compatible APIs.** Existing clients can also talk to OnlineCompiler.io through compatibility layers that are not part of this description: Judge0 CE (https://onlinecompiler.io/docs/judge0), Piston v2 (https://onlinecompiler.io/docs/piston) and Jobe for Moodle CodeRunner (https://onlinecompiler.io/docs/jobe). The MCP server and WebSocket widget are documented at https://onlinecompiler.io/docs.
Full documentation: https://onlinecompiler.io/docs'
termsOfService: https://onlinecompiler.io/terms
contact:
name: OnlineCompiler.io
url: https://onlinecompiler.io/contact
servers:
- url: https://api.onlinecompiler.io
description: Production
tags:
- name: Reference
description: Compilers, limits and health. No API key needed.
paths:
/api/compilers/:
get:
operationId: listCompilers
tags:
- Reference
summary: List the compilers and their ids
description: The current compiler ids, with display names and, for Python, the preinstalled packages. No API key needed. Use an id as `compiler` in the run endpoints.
security: []
responses:
'200':
description: The compilers.
content:
application/json:
schema:
$ref: '#/components/schemas/CompilerList'
example:
compilers:
- id: python-3.14
name: Python
packages:
- name: numpy
version: 2.5.4
- id: gcc-15
name: C
/api/limits/:
get:
operationId: getLimits
tags:
- Reference
summary: Execution limits and default account limits
description: 'Per-run limits and the default (Free) account limits. File sizes are in bytes. No API key needed. An account on a paid plan has higher account limits: see `GET /api/usage/`.'
security: []
responses:
'200':
description: The limits.
content:
application/json:
schema:
$ref: '#/components/schemas/Limits'
/api/health/:
get:
operationId: getHealth
tags:
- Reference
summary: Whether a run gets through right now
description: Checks the database and sends a one-line program through the job queue into a real sandbox. Answers 200 when every check is ok and 503 otherwise. The report is shared and reused for a minute, so `checked_at` can be up to a minute old; calling it costs no runs. Not cacheable. No API key needed.
security: []
responses:
'200':
description: Every check is ok.
headers:
Cache-Control:
schema:
type: string
description: no-store
content:
application/json:
schema:
$ref: '#/components/schemas/Health'
example:
status: ok
checked_at: '2026-10-24T10:41:07.512345+00:00'
checks:
database: ok
queue: ok
sandbox: ok
run_seconds: 0.84
'503':
description: At least one check failed.
content:
application/json:
schema:
$ref: '#/components/schemas/Health'
example:
status: down
checked_at: '2026-10-24T10:41:07.512345+00:00'
checks:
database: ok
queue: timeout
sandbox: unknown
run_seconds: null
components:
schemas:
CompilerList:
type: object
required:
- compilers
properties:
compilers:
type: array
items:
type: object
required:
- id
- name
properties:
id:
$ref: '#/components/schemas/CompilerId'
name:
type: string
description: The language's display name.
packages:
type: array
items:
type: object
required:
- name
- version
properties:
name:
type: string
version:
type: string
description: Preinstalled packages, present for compilers that ship some.
CompilerId:
type: string
description: A compiler id from GET /api/compilers/. Retired ids (the dotnet-*-9 ids, now dotnet-*-10) are still accepted and run on their successor, but are not listed.
examples:
- python-3.14
- gcc-15
- nodejs-24
enum:
- python-3.14
- python-3.14-pandas2
- duckdb-1.5
- gcc-15
- g++-15
- openjdk-25
- dotnet-csharp-10
- dotnet-fsharp-10
- php-8.5
- ruby-4.0
- haskell-9.12
- go-1.26
- rust-1.93
- typescript-deno
- nodejs-24
- sqlite-3
- bash-5.2
- gfortran-15
- dotnet-vbnet-10
- kotlin-2.4
- r-4.6
- swift-6.4
- gnucobol-3.2
- perl-5.44
- julia-1.13
- fpc-3.2
- octave-11
- nasm-3
- lua-5.5
- ocaml-5.4
- sbcl-2.6
- erlang-29
- elixir-1.20
- swipl-10
- ldc-1.43
- fbc-1.10
- dart-3.13
- clojure-1.12
- groovy-6.0
- scala-3.10
- zig-0.17
- nim-2.2
- crystal-1.22
- gnat-15
- powershell-7.6
- racket-9.3
- clang-objc-21
Limits:
type: object
properties:
memory_mb:
type: integer
cpus:
type: integer
timeout_seconds:
type: integer
processes:
type: integer
code_kb:
type: integer
input_kb:
type: integer
output_kb:
type: integer
description: Cap per stream (stdout, stderr).
submissions_per_minute:
type: integer
pending_submissions:
type: integer
running_submissions:
type: integer
submissions_per_month:
type: integer
input_files:
type: integer
input_files_bytes:
type: integer
output_files:
type: integer
output_files_bytes:
type: integer
run_tests_files_bytes:
type: integer
file_retention_days:
type: integer
file_quota_bytes:
type: integer
required:
- memory_mb
- cpus
- timeout_seconds
- processes
- code_kb
- input_kb
- output_kb
- submissions_per_minute
- pending_submissions
- running_submissions
- submissions_per_month
- input_files
- input_files_bytes
- output_files
- output_files_bytes
- run_tests_files_bytes
- file_retention_days
- file_quota_bytes
description: Defaults for a Free account; sizes in bytes where the name says bytes.
Health:
type: object
required:
- status
- checked_at
- checks
- run_seconds
properties:
status:
type: string
enum:
- ok
- down
checked_at:
type: string
format: date-time
checks:
type: object
required:
- database
- queue
- sandbox
properties:
database:
type: string
description: ok or unreachable.
queue:
type: string
description: ok, unreachable, timeout (no run within 20 seconds) or checking.
sandbox:
type: string
description: ok, busy, failed or unknown.
run_seconds:
type:
- number
- 'null'
description: How long the check's one-line program took, null when it did not run.
securitySchemes:
ApiKey:
type: apiKey
in: header
name: Authorization
description: Your API key (key type API) from https://api.onlinecompiler.io/compilers/api-keys/, sent as the bare value of the Authorization header. Do not add a Bearer prefix. A key may be restricted to an origin in the dashboard.
externalDocs:
description: OnlineCompiler.io documentation
url: https://onlinecompiler.io/docs