SpecSim — Instant OpenAPI Mock Servers with Chaos Simulation

Turn any OpenAPI 3.x spec into a fully functional mock server in seconds. Generate deterministic responses, simulate network chaos, inject latency, and test edge cases — all without writing a single line of server code.

Website: specsim.net

Key Features

Instant Mock Creation — Upload an OpenAPI spec (JSON or URL) and get a working mock server immediately
Deterministic Responses — Schema-driven response generation from your spec definitions
Chaos Simulation — Flaky mode, error storms, configurable latency and jitter
Scenario Management — Save and reuse chaos configurations per mock
Spec Validation — Validate any OpenAPI spec before mocking (free, no auth required)
Spec Diffing — Compare two OpenAPI specs to detect breaking changes
Request Logging — View recent gateway requests for debugging
Public Mock URLs — Share mock endpoints with your team without auth

Authentication

All authenticated endpoints require your RapidAPI key. When you subscribe on RapidAPI, the marketplace automatically injects the X-RapidAPI-Key and X-RapidAPI-Host headers into every request — no manual configuration needed.

Rate Limiting

Every authenticated response includes standard rate-limit headers:

Header	Description
`X-RateLimit-Limit`	Max requests allowed per 60-second window
`X-RateLimit-Remaining`	Requests remaining in the current window
`X-RateLimit-Reset`	Seconds until the rate-limit window resets
`X-Request-Id`	Unique identifier for the request (useful for support)

Exceeding the per-minute or monthly call limit returns a 429 response.

Pricing & Plan Limits

Start free, upgrade anytime. All plans are managed through RapidAPI.

Feature	Basic (Free)	Pro ($29/mo)	Ultra ($75/mo)	Mega ($199/mo)
API Calls / Month	500	25,000	250,000	2,000,000
Mock Servers	2	10	50	200
Max Spec Size	256 KB	1 MB	5 MB	10 MB
Requests / Minute	10	60	200	500
Log Retention	1 day	7 days	30 days	90 days

Overage: $0.001 per object beyond 10,240/mo included quota

Quick Start Examples

1. Health Check (No Auth Required)

curl -X GET "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/health"

Response:

{
  "ok": true,
  "service": "SpecSim",
  "timestamp": "2025-06-15T12:00:00.000Z",
  "version": "1.0.0"
}

2. Validate a Spec (No Auth Required)

curl -X POST "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/validate" \
  -H "Content-Type: application/json" \
  -d '{"url":"https://petstore.swagger.io/v2/swagger.json"}'

Response:

{
  "valid": true,
  "openapi_version": "2.0",
  "title": "Swagger Petstore",
  "paths_count": 14,
  "operations_count": 20,
  "warnings": []
}

3. Create a Mock Server

curl -X POST "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/mocks" \
  -H "x-rapidapi-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"url":"https://petstore.swagger.io/v2/swagger.json"}'

Response:

{
  "mock_id": "d4e5f6a7-b8c9-4d0e-a1f2-b3c4d5e6f7a8",
  "name": "Petstore API",
  "mock_base": "https://...mock-server/d4e5f6a7-...",
  "gateway_base": "https://...mock-gateway",
  "routes": [
    { "method": "GET", "path": "/pets", "operationId": "listPets", "summary": "List all pets" },
    { "method": "POST", "path": "/pets", "operationId": "createPet", "summary": "Create a pet" },
    { "method": "GET", "path": "/pets/{petId}", "operationId": "getPetById", "summary": "Info for a specific pet" }
  ],
  "request_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479"
}

4. List Your Mocks

curl -X GET "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/mocks" \
  -H "x-rapidapi-key: YOUR_KEY"

5. Call the Mock Gateway

curl -X POST "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/mock-gateway" \
  -H "x-rapidapi-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"mock_id":"d4e5f6a7-b8c9-4d0e-a1f2-b3c4d5e6f7a8","method":"GET","path":"/pets"}'

Response:

{
  "data": {
    "id": 42,
    "name": "Buddy",
    "tag": "dog",
    "status": "available"
  },
  "meta": {
    "matched_operation_id": "listPets",
    "matched_template": "/pets",
    "path_params": {},
    "generation_method": "schema",
    "latency_ms": 12,
    "request_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479"
  }
}

6. Create a Chaos Scenario

curl -X POST "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/scenarios/MOCK_ID" \
  -H "x-rapidapi-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"name":"chaos","mode":"flaky","error_rate":0.3,"latency_ms":500}'

Response:

{
  "scenario": {
    "id": "c1d2e3f4-a5b6-7890-cdef-1234567890ab",
    "mock_id": "d4e5f6a7-b8c9-4d0e-a1f2-b3c4d5e6f7a8",
    "name": "chaos",
    "config_json": {
      "mode": "flaky",
      "latency_ms": 500,
      "jitter_ms": 0,
      "error_rate": 0.3,
      "error_codes": [500]
    }
  },
  "request_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479"
}

7. Diff Two Specs

curl -X POST "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/diff" \
  -H "Content-Type: application/json" \
  -d '{"old_url":"https://petstore.swagger.io/v2/swagger.json","new_url":"https://petstore3.swagger.io/api/v3/openapi.json"}'

8. View Request Logs

curl -X GET "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/logs/MOCK_ID?limit=10" \
  -H "x-rapidapi-key: YOUR_KEY"

9. Delete a Mock

curl -X DELETE "https://specsim-openapi-mock-server-simulation-api.p.rapidapi.com/mocks/MOCK_ID" \
  -H "x-rapidapi-key: YOUR_KEY"

Chaos Simulation Modes

Mode	Description
`flaky`	Randomly fails a percentage of requests based on `error_rate` (0.0–1.0)
`errorstorm`	Returns errors on every request with configurable status codes
`chaos`	Random errors with random status codes from `error_codes` list

All modes support latency_ms and jitter_ms for simulating slow networks.

Error Responses

All errors follow a consistent format:

{
  "code": 401,
  "message": "Unauthorized – missing or invalid RapidAPI key",
  "request_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479"
}

Code	Meaning
400	Bad request — invalid input or missing fields
401	Unauthorized — missing or invalid API key
404	Not found — mock or resource doesn't exist
429	Rate limit exceeded — per-minute or monthly quota hit
500	Internal server error

OpenAPI Spec

The full machine-readable OpenAPI 3.0 specification is available at:
https://specsim.net/openapi.yaml

Support & Contact

Website: specsim.net
Email: specsim@fastmail.com