OpenAPI Validator
Validate, format, and summarize OpenAPI/Swagger specifications.
A powerful client-side utility to validate OpenAPI 3.0, 3.1, and Swagger 2.0 specifications without sending your data to a server. Quickly identify structural errors, format specs consistently in JSON or YAML, and generate high-level markdown summaries of your API endpoints.
Keywords: openapi validator, swagger validator, openapi formatter, swagger formatter, openapi to json, swagger to yaml, api spec validator
Tags: openapi, swagger, api, validate, format, oas, rest
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How to OpenAPI Validator Online
Paste your OpenAPI or Swagger specification into the input area. The tool automatically detects whether you are using JSON or YAML format.
Choose your preferred indentation size (2, 4, or 8 spaces) and select an output format (JSON, YAML, or Same) from the bottom options panel.
Click the Validate button or press ⌘⇧V (Mac) / Ctrl+Shift+V (Windows) to instantly check for structural errors against the official OpenAPI/Swagger specification schema.
Click Format to safely parse and rebuild your specification with clean, consistent indentation, or click Summary to generate a high-level markdown overview of your API endpoints.
You can toggle 'Auto Validate' to run checks instantly as you type. Once finished, use the Share button to generate a compressed URL for your team.
OpenAPI Validator Features
Comprehensive validation for OpenAPI 3.0, 3.1, and Swagger 2.0 schemas against the official specifications.
Intelligent format detection: Automatically identifies whether your API input is written in JSON or YAML.
Bidirectional format conversion: Validate and convert your Swagger/OpenAPI spec from JSON to YAML, or YAML to JSON with a single click.
Markdown Summary generation: Instantly extracts API paths, HTTP methods, descriptions, and parameters into a clean, readable Markdown format.
Real-time auto-validation: Toggle the auto-validate option to get instant error feedback while you edit your API specification.
Precise error reporting: Validation issues display the severity level, specific path in the object tree, and actionable error messages.
Swagger 2.0 Bundling: Includes a specialized action to bundle and upgrade legacy Swagger 2.0 specifications into formatted output.
Shareable URLs: Generates gzip-compressed URL parameters so you can safely share API specs with teammates.
Client-side execution: All API spec validation occurs in your browser. No sensitive API designs are transmitted to external servers.
Developer keyboard shortcuts: Use ⌘⇧V to validate, ⌘⇧F to format, and ⌘⇧S to generate summaries without taking your hands off the keyboard.
In-Depth Technical Guides
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Pre-built Automation Pipelines
Chain OpenAPI Validator with other utilities in a multi-step visual workflow.
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Example Input & Output
Sample ReferenceInteractive Example: OpenAPI Validator in ActionShow example
Sample Input (yaml)
openapi: 3.0.0
info:
title: Sample API
version: 1.0.0
paths:
/users:
get:
summary: List usersSample Output
[ERROR] Line 9: Path '/users' GET operation is missing required 'responses' definition.
Validated against OpenAPI 3.0.0 schema.What happened:
Performs semantic schema validation and syntax checking for OpenAPI 3.0 and Swagger 2.0 definitions.
Frequently Asked Questions
- What is an OpenAPI Validator?
- An OpenAPI Validator checks your API specification (written in JSON or YAML) against the official OpenAPI (formerly Swagger) schema. It ensures that your document is structurally correct, contains all required fields, and follows the strict rules defined by the OpenAPI Initiative.
- Does this tool support both JSON and YAML?
- Yes. The validator automatically detects the format of your input. You can paste a JSON specification and output it as YAML, or vice versa, making it an excellent bidirectional API conversion tool.
- What versions of OpenAPI are supported?
- This tool supports the modern OpenAPI 3.1.x and 3.0.x specifications, as well as the legacy Swagger 2.0 format. It uses industry-standard parsing engines to ensure 100% compliance with official specifications.
- Is my API specification data safe?
- Absolutely. Unlike many online validators that upload your API design to a cloud server, DevFlow's OpenAPI Validator processes everything locally in your browser. Your sensitive API endpoints, architectures, and documentation never leave your machine.
- What does the Summary feature do?
- The Summary action parses your complex, deeply-nested OpenAPI specification and generates a clean, high-level Markdown list of all your endpoints. It extracts the HTTP methods, paths, and operation summaries, making it perfect for copying into a README file or sharing with frontend developers.
- How do I interpret validation errors?
- When validation fails, the tool displays an 'Issues found' panel below your code. Each error specifies the severity (e.g., ERROR or WARNING), the exact object path where the issue occurred (e.g., 'paths./users.get.responses'), and a descriptive message explaining what is missing or invalid.
- Does it support multi-file OpenAPI specs with $ref?
- For security reasons and to ensure your data never leaves your browser, this online tool resolves internal local references (e.g., '#/components/schemas/User') but intentionally blocks external HTTP network references and local file system path traversal.
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