Which spec versions are supported?

OpenAPI 3.x and Swagger 2.0, in either JSON or YAML.

Does it replace a full linter like Spectral?

It covers the most common contract-quality rules. Spectral offers custom rulesets; this gives instant feedback with no install.

Is my spec uploaded anywhere?

No. Parsing and analysis run entirely in your browser.

Does it work offline and on mobile?

Yes. Once the page has loaded it keeps working without a network connection, and the layout is responsive so it stays usable on phones and tablets.

Do I need an account or an API key?

No. Every tool on Coders Hub is free to use with no sign-up, no API key and no usage limits.

API Contract Analyzer

Lint an OpenAPI or Swagger spec for contract quality issues.

Support

Works Offline

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No API

OpenAPI document

Paste JSON or YAML (OpenAPI 3.x / Swagger 2)

openapi: 3.0.3
info:
  title: Orders API
  version: 1.3.0
paths:
  /orders:
    get:
      operationId: listOrders
      summary: List orders
      tags: [orders]
      parameters:
        - name: limit
          in: query
          required: false
          schema:
            type: integer
        - name: status
          in: query
          required: true
          schema:
            type: string
      responses:
        "200":
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  type: object
                  required: [id, total, currency]
                  properties:
                    id:
                      type: string
                    total:
                      type: string
                    currency:
                      type: string
    post:
      operationId: createOrder
      summary: Create an order
      tags: [orders]
      responses:
        "201":
          description: Created
  /orders/{orderId}:
    get:
      operationId: getOrder
      summary: Get an order
      tags: [orders]
      parameters:
        - name: orderId
          in: path
          required: true
          schema:
            type: string
      responses:
        "200":
          description: OK
  /refunds:
    post:
      operationId: createRefund
      summary: Create a refund
      tags: [refunds]
      responses:
        "201":
          description: Created

Contract report

Structure, documentation and safety checks

Operations

Errors

Warnings

Notes

Orders API · v1.3.0 · parsed as YAML

servers—No `servers` declared, so clients cannot infer a base URL.
GET /orders—No 4xx error response documented.
GET /orders—No security requirement — the operation is documented as public.
POST /orders—No 4xx error response documented.
POST /orders—POST has no request body schema.
POST /orders—No security requirement — the operation is documented as public.
GET /orders/{orderId}—No 4xx error response documented.
GET /orders/{orderId}—No security requirement — the operation is documented as public.
POST /refunds—No 4xx error response documented.
POST /refunds—POST has no request body schema.
POST /refunds—No security requirement — the operation is documented as public.
info—No API description — useful for docs and SDK generation.
info—No contact details declared.
GET /orders—No tags, so docs cannot group this operation.
POST /orders—No tags, so docs cannot group this operation.
GET /orders/{orderId}—No tags, so docs cannot group this operation.
POST /refunds—No tags, so docs cannot group this operation.

About the API Contract Analyzer

Paste an OpenAPI 3 or Swagger 2 document (JSON or YAML) and get a prioritised list of contract problems: missing operationIds, undocumented responses, absent security schemes, unversioned servers, missing descriptions and error responses. Everything is parsed locally in your browser.

Examples

OpenAPI 3 spec

YAMLopenapi: 3.0.0 ...

Output

12 findings: 3 errors, 5 warnings, 4 info

Keyboard shortcuts

Copy the main outputCtrl / ⌘ + Shift + C
Download the resultCtrl / ⌘ + S
Share this toolCtrl / ⌘ + Shift + S
Reset the inputsAlt + R
Open the tool search paletteCtrl / ⌘ + K

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Frequently asked questions

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Version 1.0.0 · Updated 2026-08-20 · Runs entirely in your browser

API Contract Analyzer

About the API Contract Analyzer

Examples

Keyboard shortcuts

Related tools

API Breaking Change Detector

API Changelog Generator

API Consistency Auditor

Postman ↔ OpenAPI Converter

API Response Schema Generator

cURL Command Parser

Frequently asked questions

Which spec versions are supported?

Does it replace a full linter like Spectral?

Is my spec uploaded anywhere?

Does it work offline and on mobile?

Do I need an account or an API key?

Read more