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Tengu Decoded: what the Claude Code binary does

The article analyzes the Claude Code CLI binary (named "tengu"), documenting its inner workings, behavior, and functionality to provide transparency about what the proprietary binary does on a user's system.

Background

- Claude Code is Anthropic's terminal-based AI coding tool (released 2025) that edits files, runs shell commands, and manages development workflows autonomously. - This GitHub repo ("tengu-decoded") reverse-engineers the Claude Code binary — internally code-named "Tengu" after a Japanese mythical creature — by decompiling its executable. - The binary is a Node.js app packaged as a standalone executable with obfuscated source code and anti-tamper protections. The decoded output reveals how it calls Anthropic's API, handles tool definitions (file editing, shell access), manages authentication, and implements sandboxing. - For developers and safety researchers, this provides rare transparency into a proprietary AI agent: its architecture, built-in prompts, data collection practices, and security guardrails.

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