Run this tool instantly in your browser. No signup and no server-side processing.

OpenAPI Mock Playground

Paste an OpenAPI spec and generate mock responses for each endpoint.

OpenAPI Spec (JSON)

{
  "openapi": "3.0.0",
  "info": {
    "title": "Pet Store",
    "version": "1.0.0"
  },
  "paths": {
    "/pets": {
      "get": {
        "summary": "List all pets",
        "responses": {
          "200": {
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "type": "object",
                    "properties": {
                      "id": {
                        "type": "integer",
                        "example": 1
                      },
                      "name": {
                        "type": "string",
                        "example": "Buddy"
                      },
                      "tag": {
                        "type": "string",
                        "example": "dog"
                      }
                    }
                  }
                }
              }
            }
          }
        }
      },
      "post": {
        "summary": "Create a pet",
        "responses": {
          "201": {
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "id": {
                      "type": "integer"
                    },
                    "name": {
                      "type": "string"
                    },
                    "created": {
                      "type": "string",
                      "format": "date-time"
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Endpoints (0)

Related Tools

OpenAPI Viewer

Paste an OpenAPI/Swagger JSON spec to visualize your API endpoints.

HTTP Request Builder

Build HTTP requests visually and generate cURL, JavaScript fetch, or Python code.

JSON Formatter

Format, validate, and minify JSON payloads instantly.

cURL to Code

Convert cURL commands to JavaScript, Python, Go, PHP, or Rust code.

OpenAPI Mock Playground: complete usage guide

Generate mock JSON responses from OpenAPI specs so frontend and QA teams can test flows before backend completion.

What this tool does

It parses OpenAPI schema definitions and extracts supported endpoints.

It derives mock response bodies from response schemas and examples.

It resolves simple `$ref` schema links via definitions/components maps.

It provides selectable endpoint mock output with copy-ready JSON.

Typical use cases

Unblock frontend screens while backend endpoints are in progress.
Create deterministic API fixtures for integration and UI tests.
Validate schema completeness by inspecting generated mock objects.
Share representative responses in feature planning discussions.
Prototype API clients without requiring a running mock server.

Input examples

OpenAPI JSON

{ "openapi": "3.0.0", "paths": { ... } }

Schema example

properties id integer, name string, created date-time

Response target

200/201 application/json schema blocks

Output examples

Endpoint list

GET /pets, POST /pets with summaries

Mock object

{ "id": 1, "name": "Buddy", "tag": "dog" }

Generated defaults

email, uuid, date-time, uri formats mapped to sample values

Common errors and fixes

Invalid JSON spec input

Fix syntax and confirm valid OpenAPI structure.

Response schema not detected

Add JSON schema under `responses` content blocks.

Unexpected null mock output

Define explicit types/properties for schema nodes.

Reference resolution misses schema

Confirm `$ref` names exist in definitions/components.

Mocks differ from production behavior

Treat generated output as scaffolding and validate with backend contracts.

Security and privacy notes

Mock generation runs locally in your browser session.
Avoid sharing internal API schemas outside approved channels.
Review generated examples for accidental sensitive sample values.

Step-by-step workflow

Start with a minimal input for OpenAPI Mock Playground and verify baseline behavior first.
Make assumptions explicit: encoding, delimiter strategy, and timezone.
Change one variable at a time and compare output diffs.
Keep one verified output snapshot as a team reference.

Quality checklist before sharing output

Confirm OpenAPI Mock Playground output is deterministic across repeated runs with identical input.
Check boundary inputs (empty values, long fields, invalid characters).
Remove sensitive data before sharing output externally.
Verify final rendering on both desktop and mobile viewports.