Scheme, evaluated over HTTP.

Send source to one endpoint. Get back the value of every top-level form, stdout, CPU-time stats and structured errors, from a fresh sandbox on every request.

Get an API key Read the docs

Endpoint: POST /v1/eval
Language: Scheme, R7RS subset
Isolation: Fresh process per request
Billing: Per CPU-millisecond

POST /v1/demo

1(define (fact n)
2  (if (= n 0) 1 (* n (fact (- n 1)))))
3 
4(fact 10)
5(fact 30)

⌘↵to run

idle

; press Run to evaluate each top-level form

cpu: —
wall: —
steps: —

01Integrate

One endpoint. Any language that speaks HTTP.

Send JSON with a bearer key. A program that ran always comes back as 200 with its outcome in status, so an HTTP error only ever means the request itself was wrong.

Printed values exact for every type, bignums included
A typed JSON copy of numbers, strings, booleans and lists
RateLimit headers on every evaluation

curl -sS https://api.cons.stneto.dev/v1/eval \
  -H "Authorization: Bearer $CONS_KEY" \
  -H "Content-Type: application/json" \
  -d '{"source": "(define (sq x) (* x x))\n(map sq (list 1 2 3))"}'

const res = await fetch("https://api.cons.stneto.dev/v1/eval", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.CONS_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({ source: "(map (lambda (x) (* x x)) '(1 2 3))" }),
});
const { status, results, error } = await res.json();
console.log(status, results.at(-1)?.json); // ok [1, 4, 9]

import os, requests

res = requests.post(
    "https://api.cons.stneto.dev/v1/eval",
    headers={"Authorization": f"Bearer {os.environ['CONS_KEY']}"},
    json={"source": '(string-append "hello, " "world")', "timeout_ms": 2000},
)
body = res.json()
print(body["status"], body["results"][-1]["json"])  # ok hello, world

200 OK · application/json

{
  "status": "ok",
  "results": [
    {"index": 0, "line": 1, "col": 1, "value": null, "json": null},
    {"index": 1, "line": 2, "col": 1, "value": "(1 4 9)", "json": [1, 4, 9]}
  ],
  "stdout": "",
  "stats": {"wall_ms": 0.21, "cpu_ms": 0.02, "steps": 25},
  "error": null,
  "request_id": "req_8k2j4h5g6f7d8s9a0p1o"
}

02Runtime

Built to run code you didn't write.

Programs from your users, from an LLM, from a config file. Each one runs isolated, with limits you can see before you hit them.

A fresh sandbox per request: Each program starts from a clean environment in its own process. Nothing is shared between requests.
A result for every form: Each top-level form returns its printed value, a typed JSON copy, and the line and column it came from.
Structured errors: Errors carry a stable type to match on, a message, and the form, line and column that failed.
Billed by CPU time: Waiting for a slot costs nothing. Each request is charged the CPU it used, rounded up to the millisecond.
Hard limits: Wall-clock timeouts, step and memory caps and integer size limits stop runaway programs early.
OpenAPI spec: Generate a client from the spec, or read the endpoint docs built from it.

03Lifecycle

What happens to a request.

Every check that can turn a request away runs before your program does, and each one answers with its own status and error type.

01
Authenticate
The bearer key is checked and the body validated.
401422
02
Rate limit
Requests per minute per key, then evaluations in flight per account.
429
03
Reserve CPU
The timeout is reserved against the month's CPU allowance up front.
429
04
Evaluate
A fresh process runs the program under step, memory and time limits.
503
05
Settle
The reservation settles to the CPU used, and the response goes out.
200

04Pricing

Pay for CPU, not for waiting.

Each request is charged max(1, ceil(cpu_ms)). Time spent queued or blocked isn't, and failed programs pay only for the CPU they used.

See pricing and limits

Free every month, on every plan: 600CPU-s
Billing granularity: 1ms
Charged for time spent queued: 0ms

> (eval 'your-program)

Start evaluating Scheme today.

Create an account Quickstart

Scheme, evaluated over HTTP.

One endpoint. Any language that speaks HTTP.

Built to run code you didn't write.

What happens to a request.

Authenticate

Rate limit

Reserve CPU

Evaluate

Settle

Pay for CPU, not for waiting.

Start evaluating Scheme today.