What is Kraube API?

Kraube API is a lightweight Go gateway for accessing the Anthropic Messages API through your Claude Pro/Max/Team subscription via OAuth.

Why

The official Anthropic Go SDK requires a paid API key. If you have a Claude subscription, you're already paying — but there's no official library to use your subscription programmatically from Go.

Kraube API solves this by replicating the Claude Code CLI's HTTP protocol: billing headers, metadata, beta headers, and Chrome TLS fingerprinting.

Key Principles

OAuth-only

The only authentication method is OAuth Bearer token via claude.ai subscription. No API keys.

Stateless

The client doesn't know where tokens come from. Everything goes through the TokenProvider interface — a single method. File, env variable, Vault, Redis, callback — any source works.

Lightweight

Minimal wrapper over HTTP. Not a framework, not an SDK with abstractions — just a typed HTTP client. You bring your own architecture.

Reverse-engineered

The protocol is taken from reverse engineering the Claude Code CLI binary. When something isn't documented in the Anthropic API docs, the CLI binary is the source of truth.

What it supports

• Streaming and non-streaming requests
• Tool use (custom + built-in: web search, code execution, text editor, bash)
• Extended thinking (enabled, adaptive, disabled)
• Vision (images via URL and base64)
• Documents
• System prompts with caching
• Structured output (JSON Schema)
• Token counting
• Rate limit tracking