# 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 > Canonical page: https://elysiatools.com/en/tools/api-contract-stress-tester - **Category:** Development - **Keywords:** openapi, api contract, boundary testing, schema validation ## Overview 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. ## Inputs - **OpenAPI Specification** (textarea): Paste an OpenAPI 3.x YAML or JSON document here... - **Base URL** (text): https://api.example.com - **Execute Real Requests** (checkbox) - **Authorization Header** (text): Bearer - **Maximum Cases Per Field** (number) - **Request Timeout (ms)** (number) ## 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. ## Frequently asked questions ### 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 ', in the Authorization Header field to authenticate the generated requests. ### Does it test all types of request parameters? 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