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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
Development
Input Types
textarea, text, checkbox, number
Output Type
json
Sample Coverage
4
API Ready
Yes

Overview

The API Contract Stress Tester automatically generates boundary-value test cases directly from your OpenAPI 3.x specifications. It evaluates schema constraints like minimum lengths, enums, and required fields to build edge-case payloads, and can optionally execute these requests against a live backend to identify contract mismatches and validation failures.

When to Use

  • •When validating that a newly developed API endpoint strictly adheres to its OpenAPI 3.x schema definitions.
  • •Before deploying backend changes to ensure existing validation logic handles edge cases and invalid inputs correctly.
  • •When auditing third-party APIs to discover undocumented constraints or contract violations.

How It Works

  • •Paste your OpenAPI 3.x specification (YAML or JSON) into the primary input field.
  • •Adjust the maximum number of test cases generated per field to control the strictness of the boundary testing.
  • •Optionally provide a Base URL and Authorization header, then enable 'Execute Real Requests' to test a live server.
  • •Review the generated JSON report detailing the generated cases, executed requests, and any contract mismatches found.

Use Cases

Generating a comprehensive suite of negative test cases for a user registration endpoint to ensure invalid emails and under-age inputs are rejected.
Running automated contract checks against a staging environment to verify that the backend implementation matches the documented API design.
Stress testing an e-commerce checkout API by sending boundary values for item quantities and price fields.

Examples

1. Generating boundary cases for a signup API

QA Engineer
Background
A QA engineer needs to write test cases for a new user registration endpoint but wants to save time on manual test design.
Problem
Manually identifying all edge cases for email lengths, role enums, and age minimums is tedious and prone to human error.
How to Use
Paste the OpenAPI YAML containing the /users POST route, leave 'Execute Real Requests' unchecked, and set 'Maximum Cases Per Field' to 3.
Example Config
maxCasesPerField: 3, executeRequests: false
Outcome
The tool outputs a JSON array of edge-case payloads, such as missing required fields or invalid enum members, ready to be imported into a testing framework.

2. Spotting contract mismatches on a staging server

Backend Developer
Background
A developer just updated the validation logic for a product inventory API and deployed it to a staging environment.
Problem
The developer needs to verify that the staging server correctly rejects invalid payloads according to the OpenAPI spec without writing custom scripts.
How to Use
Paste the OpenAPI JSON, enter the staging Base URL, input a Bearer token in the Authorization Header, and check 'Execute Real Requests'.
Example Config
baseUrl: 'https://staging-api.example.com', executeRequests: true, authorizationHeader: 'Bearer abc123xyz'
Outcome
The tool sends the generated boundary payloads to the staging server and returns a JSON summary highlighting any endpoints where the server's response violated the expected contract.

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FAQ

What versions of OpenAPI are supported?

This tool specifically supports OpenAPI 3.x specifications in both YAML and JSON formats.

Does the tool actually send requests to my server?

Only if you enable the 'Execute Real Requests' option and provide a valid Base URL. Otherwise, it only generates the test cases locally.

How does it generate boundary values?

It reads schema constraints like minLength, maximum, enum, and required arrays to create payloads that test the exact limits and invalid states of your API.

Can I test authenticated endpoints?

Yes, you can provide an Authorization header (e.g., Bearer token) to authenticate the generated requests against your backend.

What is the maximum timeout for real requests?

You can configure the request timeout up to 30,000 milliseconds (30 seconds) per request.

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]