Introduction

Impostor is a fast, local API client for macOS and Windows. It does what you reach for Postman to do — build and send HTTP requests, organise them, script around them, talk WebSocket/SSE/gRPC/MCP — but it is built to be small and quick, with native performance instead of a heavyweight Electron runtime.

Why Impostor

• Native and fast. A Rust core with an OS-native webview, not Electron. Cold start and memory footprint are a fraction of the usual API clients.
• Local-first. Your workspace is just a folder of human-readable YAML files — one request per file. No account, no cloud, no telemetry. Commit it to git and diff/review/branch your API collection like any other code.
• Secrets stay safe. Sensitive values are stored encrypted on your device — unlocked by your OS keychain — never on disk in plain text.
• Beyond REST. WebSocket, Server-Sent Events, gRPC, and MCP (the Model Context Protocol) are first-class request types, not bolted-on extras.
• Scriptable and AI-ready. Drive any saved request from a headless command line, or let a local AI agent list, inspect, and run your requests through the built-in MCP server — the same resolver and engine as the app.

How the docs are organised

• Getting started — install Impostor and send your first request.
• Building requests — the request editor, environments & variables, scripting, and authentication.
• Protocols — WebSocket, SSE, gRPC, and MCP.
• Workflows — the collection runner, the command line, driving Impostor from AI, team sync over git, importing from Postman/cURL, code generation, and cookies.
• Reference — TLS & certificates, the workspace storage format, and keyboard shortcuts.

New here?

Head to Getting started to install the app, open a workspace, and send your first request. Prefer to learn by example? Clone the support repo — a ready-to-open workspace covering every feature, with a one-command mock backend included.