v1.0 — now with agent sandbox mode

Fake APIs.
Real tests.
No credits burned.

Spin up realistic mock API endpoints in 12 seconds. Test AI agents safely, mock third-party services, and stop melting your OpenAI budget on every CI run.

~/agent-test — bash
$ afs new "stripe checkout response"
✓ endpoint created
https://api.afakeserver.com/v1/k3p9xq
$ curl $ENDPOINT
{
  "id": "cs_test_a1B2c3D4e5",
  "amount_total": 2999,
  "currency": "usd",
  "payment_status": "paid",
  "customer": "cus_NffrFeUfNV2Hib",
  "livemode": false
}
$
trusted by teams testing agents at
Northwind Labs Helios.ai Drafthouse Forge Robotics Stonecutter
what it does

Everything you need to test without touching production.

// 01

AI-generated responses

Describe the shape in plain English. Get a working endpoint with realistic, varied responses. No JSON schema gymnastics.

// 02

Agent sandbox mode

Give your LLM agent a full fake universe of APIs. Let it call, fail, retry, hallucinate — without breaking anything real.

// 03

Mock third-party APIs

Pre-built fakes for Stripe, Twilio, Slack, OpenAI, and 40+ services. Latency simulation and rate-limit chaos included.

// 04

Failure injection

Test how your agent handles 500s, timeouts, malformed JSON, and rate limits. Bake resilience in from day one.

// 05

Prompt injection harness

Return adversarial payloads to probe agent robustness. Catch jailbreaks and unsafe behavior in CI, not production.

// 06

Persistent state

Stateful endpoints that remember. POST a user, GET it back. Run full integration flows without spinning up a real DB.

how it works

Three steps. Then back to building.

01

Describe what you need

"Give me a fake CRM with 500 contacts." "Mock a flaky payments API." Plain English in, working endpoint out.

02

Point your code at it

Swap one base URL. We give you a dedicated subdomain. Latency, errors, and edge cases — all tunable from a dashboard.

03

Ship with confidence

Snapshot the fixture. Replay it in CI. Catch regressions before they cost you credits — or customers.

pricing

Free to start. Honest when you scale.

Hacker
For tinkering and side projects
$0/forever
  • 3 endpoints
  • 1,000 requests / month
  • Community support
  • Public endpoints only
Team
For shipping AI products
$99/month
  • Everything in Pro
  • 5M requests / month
  • Shared workspaces
  • SSO + audit logs
  • Custom domains
  • Dedicated support

Stop testing agents in production.
Your future self will thank you.

no credit card · 12 seconds to first endpoint · cancel anytime