Siren

Siren is a lightweight, cross-platform HTTP testing application. It's a local-first alternative to Postman that works entirely offline with no account required — everything stays on your machine.

Key Features

Full HTTP Method Support

Test any HTTP endpoint with support for GET, POST, PUT, DELETE, PATCH, HEAD, and OPTIONS methods. Siren handles URI construction, automatic protocol normalization, and configurable timeouts.

Request Body Types

Compose requests with multiple body formats:

• Raw JSON/Text — Monaco editor with syntax highlighting
• Form Data — URL-encoded key-value pairs
• Multipart Form Data — File attachments and mixed content
• Binary — Raw binary payloads

Authentication

Built-in support for common authentication schemes:

• Bearer Token — JWT and custom bearer tokens
• Basic Auth — Username and password with base64 encoding
• API Key — Custom header-based API keys

Variables and Environments

Manage dynamic values across requests without manual editing:

• Global variables — Available across all requests
• Environment-specific variables — Group variables by environment (dev, staging, production)
• Variable substitution — Use in URLs, headers, body, and query parameters
• Dynamic variables — Built-in generators: , , , ,
• Secret variables — Encrypted values integrated with system secure storage (Keychain, Credential Manager)

Collections

Organize related requests into reusable groups:

• Save and manage frequently used request configurations
• Import from OpenAPI/Swagger, cURL commands, Postman collections, and Bruno collections
• Export as JSON or cURL commands

Response Analysis

Inspect every aspect of HTTP responses:

• Status codes with visual indicators and reason phrases
• Response headers with copy-to-clipboard
• Body viewer — JSON (formatted), HTML, plain text, raw binary
• Cookies — View and inspect response cookies
• Performance metrics — DNS lookup, TCP connection, TLS handshake, request send, TTFB, content download
• Network info — Local/remote IP, TLS protocol, cipher suite, certificate details
• Payload size — Request and response size breakdown

Import and Export

Move data in and out of Siren:

• cURL — Import commands and generate them from requests
• HAR — Export in HTTP Archive format
• OpenAPI/Swagger — Import API definitions to generate request collections
• JSON — Export collections and history

Mock Server

Embedded HTTP listener for local testing without external dependencies:

• Create and manage mock server configurations
• Automatic port selection with fallback range
• Request logging for all received requests
• Variable substitution in mock responses

Request History

Every request is automatically recorded:

• Search and filter past requests by method, URL, status, and timestamp
• Export full history or individual requests
• Configurable storage — option to omit request/response content for privacy

Cookie Management

Automatic cookie handling with domain, path, and expiration rules.

Retry Logic

Configurable retry attempts with smart backoff — retries on 5xx server errors but not 4xx client errors.

MCP Server Mode

Run Siren as a stdio-based MCP server for integration with Claude Desktop and other AI tools:

• Send HTTP requests programmatically
• Query request history and collections
• Manage variables and settings

Plugin System

Extend Siren's functionality with plugins loaded from the plugins directory.

Architecture

Siren is built on .NET with Blazor and uses Hermes for cross-platform desktop hosting. All data is stored locally in LiteDB with no cloud dependencies. It uses the Mythetech Framework for settings, secrets, message bus, and plugin infrastructure.

Getting Started

Visit the Siren GitHub Repository for installation and usage instructions.