# API Response Contract Validator

Validate a real API response JSON against the response schema declared in an OpenAPI 3.x specification

> Canonical page: https://elysiatools.com/en/tools/api-response-contract-validator

- **Category:** Development

- **Keywords:** openapi, api contract, response validation, schema, consumer driven contract

## Overview

Paste an OpenAPI 3.x document plus one actual API response payload, then point the validator at the path, method, and status code you want to check. The tool resolves the matching response schema and highlights missing fields, type mismatches, enum problems, and undocumented fields.

How to use it:
- OpenAPI Spec: paste YAML or JSON spec content
- Response JSON: paste the actual runtime response payload
- Path / Method / Status Code: identify the operation and response branch to validate
- Spec Format: leave auto unless you know the spec format already
- Disallow Additional Properties: raise warnings for payload fields that are not documented in the schema

## Inputs

- **OpenAPI Spec** (textarea): openapi: 3.0.3 paths: /users/{id}: ...
- **Response JSON** (textarea): {"id":1,"name":"Alice"}
- **Path** (text): /users/123
- **Method** (select)
- **Status Code** (text): 200
- **Spec Format** (select)
- **Disallow Additional Properties** (checkbox)

## When to use

- When verifying that a backend API implementation matches the documented OpenAPI specification before deploying to production.
- When debugging frontend integration issues caused by unexpected or missing fields in an API response.
- When auditing legacy APIs to identify undocumented fields being returned in production payloads.

## How it works

- Paste your OpenAPI 3.x specification (in YAML or JSON format) and the actual JSON response payload you want to validate.
- Specify the endpoint path, HTTP method, and status code to locate the exact response schema within your OpenAPI document.
- Optionally enable the 'Disallow Additional Properties' setting to flag any fields in the payload that are not explicitly defined in the schema.
- The tool parses the specification and outputs an HTML report highlighting schema violations, type mismatches, and missing required fields.

## Use cases

- Validating a newly developed API endpoint against its design-first OpenAPI contract.
- Troubleshooting a broken frontend application by checking if the backend response violates the expected schema.
- Writing consumer-driven contract tests and needing a quick manual validation of a specific endpoint's payload.

## Frequently asked questions

### Does this tool support OpenAPI 2.0 (Swagger)?

No, this validator specifically requires OpenAPI 3.x specifications to resolve response schemas accurately.

### Can I validate YAML and JSON specifications?

Yes, the tool accepts both YAML and JSON formats. You can set the format manually or leave it on 'Auto' for automatic detection.

### What does 'Disallow Additional Properties' do?

It enforces strict validation by throwing warnings if the response JSON contains fields that are not documented in the OpenAPI schema.

### How do I format the path input?

Enter the actual request path, such as /users/123. The tool will match it against the templated paths in your OpenAPI specification.

### Can I validate error responses?

Yes, simply enter the corresponding error status code (like 400 or 404) to validate the payload against that specific error schema.

## Related tools

- [JSON Schema Generator](https://elysiatools.com/en/tools/json-schema-generator): Infer JSON Schema from sample JSON, optionally merge manual schema edits, and validate data against the active schema
- [OCR PDF to Structured JSON Bridge](https://elysiatools.com/en/tools/ocr-pdf-to-structured-json-bridge): Extract the PDF text layer with geometry (lines by y-position, tables by column gaps, headings by font size, colon key-value pairs), then fill a user-supplied JSON Schema field by field — labels matched by normalized keys, values coerced to declared types and validated with ajv.
- [Short URL + UTM + QR Bundle Builder](https://elysiatools.com/en/tools/short-url-utm-builder-qr-bundle): One pass replaces bit.ly + Campaign URL Builder + QR generator: GA4-validated UTM parameters, a deterministic self-hosted short link (FNV-1a base62 slug), QR pair, redirect snippets and a tracking CSV row.
- [Train/Test Split with Stratification](https://elysiatools.com/en/tools/train-test-split-with-stratification): Class-stratified train/validation/test split or stratified k-fold for CSV/JSON datasets — seeded, reproducible, with distribution reports, leakage checks, SMOTE preview and CSV export.
- [JSON Schema Validator](https://elysiatools.com/en/tools/json-schema-validator): Validate JSON data against a JSON Schema to verify structure and data types
- [JSONPath REPL Playground](https://elysiatools.com/en/tools/jsonpath-repl-playground): An interactive JSONPath REPL that runs multi-step query pipelines against any JSON. Write one JSONPath expression per line (e.g. $..book\[?(@.price<10)\] then $\[0:5\]) and see each step's matches with counts, paths, and values — plus a shareable URL that encodes your data and pipeline. Supports recursive descent ($..), wildcards (\[*\]), filters (\[?(@.price<10)\]), slices (\[0:5:2\]), and negative indices.
- [OpenAPI to Postman Collection](https://elysiatools.com/en/tools/openapi-to-postman-collection): Turn an OpenAPI 3.x or Swagger 2.0 spec (JSON/YAML) into an importable Postman Collection v2.1.0 with folders, variables, auth and example responses.
- [OpenAPI to TypeScript Generator](https://elysiatools.com/en/tools/openapi-to-typescript-generator): Convert OpenAPI or Swagger JSON/YAML specs into TypeScript API types, request payloads, and response models with configurable output and naming styles

## Samples

- [Postman Collections - API Testing](https://elysiatools.com/en/samples/postman-collections): Comprehensive Postman collection examples including API testing, automation scripts, environment variables, mock servers, and advanced testing patterns for REST APIs
- [AWS EventBridge Samples](https://elysiatools.com/en/samples/eventbridge-samples): AWS EventBridge examples including event buses, rules, targets, schema registry, custom events, and cross-account event routing for serverless event-driven architecture
- [OpenAPI/Swagger Samples](https://elysiatools.com/en/samples/openapi-swagger): Comprehensive API documentation examples using OpenAPI 3.0 and Swagger specifications for RESTful services
- [Distributed Tracing Samples](https://elysiatools.com/en/samples/distributed-tracing-samples): Comprehensive distributed tracing examples using Jaeger, OpenTelemetry, and other modern observability tools for microservices architecture

## Related content

- [API Contract Definition, Schema Validation, and Change Testing](https://elysiatools.com/en/hubs/api-contract-testing): Define an API contract, validate schemas and captured payloads, detect compatibility risks, and record test acceptance.
- [API Versioning and Breaking Change Review](https://elysiatools.com/en/hubs/api-versioning-breaking-change-review): Compare API versions, plan migrations, and accept compatibility before release. These tools do not replace real deployment or runtime monitoring.
- [JSON Utility, Inspection, and Transformation Tools](https://elysiatools.com/en/hubs/json-utility): Format, inspect, compare, merge, transform, validate, analyze, and watermark JSON payloads for API and data workflows.
- [JSON Schema and API Contract Validation Tools](https://elysiatools.com/en/hubs/json-validate): Compare JSON schema validation, OpenAPI response checks, mutation testing, stress testing, and breaking-change detection tools in one hub for API contract review.