MockResponse

Every external system.
Instantly sandboxed.

Give your software and AI agents isolated, stateful versions of the services they depend on.

Build integrations, run tests and evaluate agents against realistic third-party systems — without production credentials, unreliable vendor sandboxes or hand-built mocks.

  • Stateful by default
  • Isolated environments
  • Deterministic resets
  • Failure simulation
A GET initially returns plan: free. After the subscription update, the same request returns plan: pro.

Mocks return responses.MockResponse runs systems.

A static mock can tell you what GET /customers/123 should return. MockResponse remembers that you created customer 123 in the first place.

Start with a sandbox template

Pre-built synthetic versions of the external systems your software depends on. Install a system, not a pile of endpoints.

240+ systems modeled — and growing

From Stripe and Slack to Salesforce, GitHub, Google Workspace and more.

130,000+ API operations

Simulate failures. Reset.
Run them in parallel.

Arm rate limits and failed payments, reset to a known world, and give each run its own copy.

Reproduce failures. Every environment can start from the same data and conditions, making agent failures debuggable instead of anecdotal. Test the dangerous paths. Expired credentials. Rate limits. Failed payments. Missing resources. Network latency. See how your agent behaves before your users do. Run in parallel. Give every run its own environment so they do not overwrite each other.

1 of 3

Reproduce failures

Every environment can start from the same data and conditions, making agent failures debuggable instead of anecdotal.

The run

  1. Agent

  2. Look up AdaOk

  3. Upgrade planFailed

    Landed on free

  4. Charge cardFailed

    Charge skipped

Reset

Same starting world. The errors can happen again.

The replay

  1. Agent

  2. Look up AdaOk

  3. Upgrade planFailed

    plan_mismatch · wanted pro · wrote free

  4. Charge cardFailed

    charge_skipped · reason still on free

The same errors come back. Now you can debug them.

If it has an API,
make it a sandbox.

Can't find the system you need? Import an OpenAPI, GraphQL, or SOAP specification. MockResponse analyzes the API's resources, operations and relationships to generate a connected environment rather than a collection of disconnected endpoints.

openapi.yaml→Resources + relationships→Stateful environment→Ready to build against

Start with the API definition. Let MockResponse build the world behind it.

  • Model resources
  • Infer relationships
  • Build starting state
  • Keep the contract deterministic

One environment for every
external dependency.

Real applications rarely depend on one external system. They depend on dozens.

MockResponse is building a common simulation layer for the external services your software depends on — giving developers, CI pipelines and agents a controlled version of the world outside their application.

Payments, CRM, messaging, identity, commerce, communication, AI, and infrastructure dependencies all connect into one isolated MockResponse environment.

From local development
to CI and agent evaluations.

  • Local development

    Stop registering for test accounts and manually maintaining fixture data just to build an integration.

  • Integration testing

    Test real workflows against deterministic environments that reset on demand.

  • CI/CD

    Remove unreliable third-party services from your test pipeline.

  • AI agents

    Give autonomous software realistic systems to operate against without giving it production access.

  • Demos & development environments

    Create complete, populated external environments without maintaining bespoke infrastructure.

Frequently asked questions

Everything you need to know before creating your first sandbox. Can't find your answer? Talk to us.

Stop mocking endpoints.
Start sandboxing systems.

Create a sandbox and point your app at it.

No production credentials required.