API Contract Stress Tester

Generate boundary-value test cases from an OpenAPI 3.x document and optionally send them to a real backend to spot contract mismatches

Paste an OpenAPI 3.x document into "OpenAPI Specification". Both YAML and JSON are supported.

What to provide:

  • A valid OpenAPI 3.x document with paths, parameters, request bodies, and responses
  • Optional schema refs under components.schemas for request-body dereferencing
  • Optional Base URL if you want the tool to send the generated boundary cases to a real backend

How the fields work:

  • OpenAPI Specification: paste the full YAML or JSON contract
  • Base URL: leave empty for offline case generation, or enter something like https://api.example.com to execute requests
  • Execute Real Requests: when enabled, the tool sends generated invalid or edge-case requests to the Base URL
  • Authorization Header: optional raw header value such as Bearer
  • Maximum Cases Per Field: limits how many boundary cases are generated for each parameter or request-body field
  • Request Timeout (ms): caps how long each real request can run before aborting

What gets tested:

  • Missing required fields
  • Empty strings, too-short strings, and too-long strings
  • Invalid enum values
  • Numbers below minimum or above maximum
  • Wrong scalar or array types for documented fields

Notes:

  • If Execute Real Requests is off, the tool only generates a contract-focused test plan.
  • If Execute Real Requests is on, the report marks whether each observed HTTP status is documented in the OpenAPI responses.
  • Path, query, header, and JSON body fields are covered; the current version focuses on application/json request bodies.

Example Results

1 examples

Generate boundary cases for a signup API

Review minLength, enum, and numeric constraints before wiring a mock server or CI contract check.

{
  "summary": {
    "endpoints": 1,
    "generatedCases": 7,
    "executedCases": 0,
    "mismatches": 0
  },
  "cases": [
    {
      "fieldPath": "body.email",
      "title": "Missing required field"
    },
    {
      "fieldPath": "body.role",
      "title": "Invalid enum member"
    }
  ]
}
View input parameters
{ "openApiSpec": "openapi: 3.0.0\npaths:\n /users:\n post:\n requestBody:\n required: true\n content:\n application/json:\n schema:\n type: object\n required: [email, role]\n properties:\n email: { type: string, minLength: 5 }\n role: { type: string, enum: [admin, member] }\n age: { type: integer, minimum: 18 }\n responses:\n \"201\": { description: created }\n \"400\": { description: bad request }\n", "executeRequests": false, "maxCasesPerField": 3 }

Key Facts

Category
Developer & Web
Input Types
textarea, text, checkbox, number
Output Type
json
Sample Coverage
4
API Ready
Yes

Overview

The API Contract Stress Tester is a developer utility that automatically generates boundary-value test cases from an OpenAPI 3.x document. By parsing your YAML or JSON specification, it creates edge-case requests to validate constraints like missing required fields, invalid enums, and out-of-bounds numbers. You can use it offline to generate a comprehensive test plan or connect it to a real base URL to execute requests and instantly spot undocumented HTTP responses and contract mismatches.

When to Use

  • •When you need to verify that your backend correctly enforces the validation rules defined in your OpenAPI specification.
  • •Before deploying a new API version to ensure edge cases like missing fields or invalid data types are handled gracefully.
  • •When auditing an existing API to discover undocumented error responses or missing schema constraints.

How It Works

  • •Paste your OpenAPI 3.x YAML or JSON document containing paths, parameters, and request bodies.
  • •Configure the maximum number of test cases per field and optionally provide a Base URL and Authorization Header for live testing.
  • •Choose whether to generate an offline test plan or execute real requests against your backend.
  • •Review the generated JSON report to identify contract mismatches, unhandled edge cases, and undocumented HTTP status codes.

Use Cases

Automatically generating negative test suites for CI/CD pipelines based on OpenAPI contracts.
Stress testing API endpoints with boundary values to ensure robust error handling and input validation.
Identifying discrepancies between API documentation and actual backend behavior during integration testing.

Examples

1. Validating a User Registration API

Backend Developer
Background
A developer has just finished implementing a new user registration endpoint and documented it using OpenAPI 3.0.
Problem
They need to ensure the API correctly rejects invalid inputs like short passwords, missing emails, and invalid roles without writing dozens of manual tests.
How to Use
Paste the OpenAPI YAML into the specification field, set 'Execute Real Requests' to false, and set 'Maximum Cases Per Field' to 3.
Example Config
{
  "executeRequests": false,
  "maxCasesPerField": 3
}
Outcome
The tool generates a JSON report detailing specific boundary cases, such as omitting the email field or sending an unregistered enum value for the role, which can be used to build automated tests.

2. Live Contract Testing for a Staging Environment

QA Engineer
Background
A QA engineer is testing a staging environment to ensure the API behaves exactly as documented in the OpenAPI spec.
Problem
They need to find out if the API returns any undocumented HTTP status codes when fed invalid data.
How to Use
Paste the OpenAPI JSON, enter the staging server's Base URL, provide a Bearer token in the Authorization Header, and enable 'Execute Real Requests'.
Example Config
{
  "baseUrl": "https://staging-api.example.com",
  "executeRequests": true,
  "authorizationHeader": "Bearer abc123xyz",
  "timeoutMs": 5000
}
Outcome
The tool sends the generated edge-case requests to the staging server and outputs a report highlighting any responses (like a 500 Internal Server Error) that are not defined in the OpenAPI responses section.

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FAQ

Does this tool support both YAML and JSON OpenAPI specs?

Yes, you can paste either a YAML or JSON OpenAPI 3.x document into the specification field.

Can I use this tool without sending real requests to my server?

Absolutely. If you leave the 'Execute Real Requests' option disabled, the tool will only generate a JSON test plan without making any network calls.

What kind of boundary cases are generated?

The tool generates cases for missing required fields, empty or out-of-bounds strings, invalid enum values, out-of-range numbers, and incorrect data types.

How does the tool handle authentication for live requests?

You can provide a raw header value, such as 'Bearer <token>', in the Authorization Header field to authenticate the generated requests.

Does it test all types of request parameters?

Yes, it covers path, query, header, and JSON body fields, with a primary focus on application/json request bodies.

API Documentation

Request Endpoint

POST /en/api/tools/api-contract-stress-tester

Request Parameters

Parameter Name Type Required Description
openApiSpec textarea Yes -
baseUrl text No -
executeRequests checkbox No -
authorizationHeader text No -
maxCasesPerField number No -
timeoutMs number No -

Response Format

{
  "key": {...},
  "metadata": {
    "key": "value"
  },
  "error": "Error message (optional)",
  "message": "Notification message (optional)"
}
JSON Data: JSON Data

AI MCP Documentation

Add this tool to your MCP server configuration: 

{
  "mcpServers": {
    "elysiatools-api-contract-stress-tester": {
      "name": "api-contract-stress-tester",
      "description": "Generate boundary-value test cases from an OpenAPI 3.x document and optionally send them to a real backend to spot contract mismatches",
      "baseUrl": "https://elysiatools.com/mcp/sse?toolId=api-contract-stress-tester",
      "command": "",
      "args": [],
      "env": {},
      "isActive": true,
      "type": "sse"
    }
  }
}

You can chain multiple tools, e.g.: `https://elysiatools.com/mcp/sse?toolId=png-to-webp,jpg-to-webp,gif-to-webp`, max 20 tools.

If you encounter any issues, please contact us at [email protected]