# HuggingFace released Tau, a coding agent > Source: > Published: 2026-07-22 12:39:37+00:00 An educational coding-agent project **Tau** is a small Python coding agent you read like a textbook. Watch it stream model output, call tools, manage sessions, and grow into a terminal UI — one readable layer at a time. No hidden machinery. Every moving part is on the page. 3-layers Provider adapters turn model responses into provider-neutral events the rest of the agent consumes. The reusable harness: messages, tools, transcript state, cancellation, queued prompts, sessions. The coding environment: files, shell, durable sessions, skills, slash commands, and a Textual TUI. no black boxes Tau answers the questions tutorials skip: What *is* an agent loop? Where do tool calls come from? How does the transcript grow? How do sessions survive the process exiting? the boundary The whole lesson is the boundary. A reusable harness must not depend on the terminal, file paths, or Rich rendering. Those wrap the harness — they never live inside it. the skills `~/.tau/sessions` how we think One job per package. Study the provider layer, harness, and coding app on their own. The agent emits a stream you can render, test, and export — not control flow buried in callbacks. Educational, not a toy. Run it as a real terminal agent while reading the code behind it. Built phase by phase, each with notes on what was added, why, and how it fits. A map for building your own agent: start with events, add a loop, wrap it in a harness, then give it tools and a UI.