Fiddler to Swagger YAML Exporter

A Fiddler extension that exports captured HTTP sessions to OpenAPI 3.0 YAML specification (Swagger format). This tool analyzes HTTP traffic captured by Fiddler and automatically generates comprehensive API documentation.

Features

🔍 Intelligent Session Analysis

• Path Parameter Detection: Automatically identifies numeric IDs, UUIDs, MongoDB ObjectIds, and other dynamic path segments
• Parameter Type Inference: Determines parameter types (string, integer, boolean, etc.) from actual values
• Content Type Detection: Analyzes request bodies to determine content types

📋 Comprehensive Schema Generation

• JSON Schema Generation: Creates OpenAPI schemas from request/response JSON bodies
• Schema Merging: Combines multiple examples to create comprehensive schemas
• Format Detection: Identifies common formats (date-time, email, URI, etc.)
• Enum Detection: Recognizes limited value sets as enums

🔐 Security Scheme Detection

• Bearer Token Authentication: Detects Authorization: Bearer headers
• API Key Authentication: Identifies X-API-Key and custom API key headers
• Header Sanitization: Removes sensitive values while preserving structure

📊 Smart Endpoint Grouping

• Path Normalization: Groups similar endpoints (e.g., /users/123 and /users/456 → /users/{id})
• Method Consolidation: Combines multiple sessions of the same endpoint
• Response Code Aggregation: Documents all observed response codes

Installation

Prerequisites

• Fiddler Classic (tested with Fiddler 4+)
• .NET Framework 4.7.2 or higher

Install from Releases

1. Download the latest release from the Releases page
2. Extract the files to %USERPROFILE%\Documents\Fiddler2\ImportExport\
3. Restart Fiddler

Manual Installation

1. Clone this repository
2. Build the project (see Building section)
3. Copy the following files to %USERPROFILE%\Documents\Fiddler2\ImportExport\:
   • FiddlerToSwagger.dll
   • Newtonsoft.Json.dll
   • YamlDotNet.dll
4. Restart Fiddler

Usage

1. Capture Sessions: Use Fiddler to capture HTTP traffic from your API
2. Select Sessions: Choose the sessions you want to export (tip: use filters to select API calls only)
3. Export:
   • Go to File → Export Sessions
   • Select "Swagger YAML" from the format dropdown
   • Choose your output filename (.yaml or .openapi.yaml)
4. Import: Use the generated YAML file with:
   • Swagger Editor
   • Postman (Import → OpenAPI)
   • API documentation tools
   • Code generation tools

Example Output

The extension generates full OpenAPI 3.0 specifications including:

openapi: 3.0.3
info:
  title: "Your API"
  version: "1.0.0"
  description: "Generated from Fiddler sessions"
servers:
  - url: "https://api.example.com"
paths:
  /users/{id}:
    get:
      summary: "Get user"
      parameters:
        - name: id
          in: path
          required: true
          schema:
            type: integer
      responses:
        200:
          description: "Successful response"
          content:
            application/json:
              schema:
                type: object
                properties:
                  # ... generated from actual responses

Building

Prerequisites

• Visual Studio 2017 or later
• .NET Framework 4.7.2 SDK
• Fiddler Classic installed (for reference assemblies)

Build Steps

1. Clone the repository:

   git clone https://github.com/Mancy/FiddlerToSwagger.git
   cd FiddlerToSwagger

2. Restore NuGet packages:

   cd workspace
   nuget restore

3. Update Fiddler reference:

   • Copy Fiddler.exe from your Fiddler installation to the project root
   • Or update the reference path in FiddlerToSwagger.csproj

4. Build the solution:

   msbuild FiddlerToSwagger.sln /p:Configuration=Release

Dependencies

• Fiddler.exe: Reference assembly (not redistributed)
• Newtonsoft.Json 12.0.1: JSON processing and schema generation
• YamlDotNet 11.2.1: YAML serialization
• System.Web: For HTTP utility functions

Tips for Best Results

1. Filter Sessions: Export only API-related sessions for cleaner output
2. Include Variety: Capture different response scenarios (success, error cases)
3. Authentication: Include authenticated requests to capture security schemes
4. Full CRUD: Capture GET, POST, PUT, DELETE operations for complete documentation
5. Error Responses: Include 4xx and 5xx responses for comprehensive error documentation

Troubleshooting

Extension not appearing in Fiddler

• Check that all DLL files are in the ImportExport folder
• Restart Fiddler completely
• Check the Log tab for error messages
• Ensure .NET Framework 4.7.2+ is installed

Export fails or produces errors

• Ensure selected sessions contain valid HTTP traffic
• Check that sessions have response bodies for schema generation
• Try with a smaller subset of sessions first
• Check Fiddler's Log tab for detailed error messages

Empty or invalid YAML

• Verify selected sessions contain API traffic (not web pages)
• Ensure sessions have JSON request/response bodies
• Check that the sessions completed successfully (not interrupted)

Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Make your changes
4. Add tests if applicable
5. Commit your changes (git commit -m 'Add some amazing feature')
6. Push to the branch (git push origin feature/amazing-feature)
7. Open a Pull Request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• Inspired by the original FiddlerExportToPostman project
• Built with YamlDotNet for YAML serialization
• Uses Newtonsoft.Json for JSON processing
• Thanks to the Fiddler team for the extensible architecture

Related Projects

• Fiddler Classic - The HTTP debugging proxy
• OpenAPI Specification - API documentation standard
• Swagger Editor - Online OpenAPI editor
• Postman - API development platform