introducing tau τ — an educational agent harness that teaches you how to build agent harnesses

i will be publishing tutorials and demos on how to use it to create your own TUIs, harnesses, extensions, etc.

Happy Tau Day!! 🤓

👉 https://t.co/5sWxNtXTZP https://t.co/uiViXChBbw

Learn how coding agents are built.

Source: https://twotimespi.dev/ τtauv0.1

An educational coding-agent project

Tauis 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.

θ sweeps 0 → τθ = 0.00 learnagent architecture

readsmall Python layers

runa real terminal agent

01

A coding agent as a curriculum

Ⅰtau_ai

Models become streams

Provider adapters turn model responses into provider-neutral events the rest of the agent consumes.

Ⅱtau_agent

The agent loop

The reusable harness: messages, tools, transcript state, cancellation, queued prompts, sessions.

Ⅲtau_coding

It becomes useful

The coding environment: files, shell, durable sessions, skills, slash commands, and a Textual TUI.

The lesson

Every moving part is visible.

Tau answers the questions tutorials skip: Whatisan agent loop? Where do tool calls come from? How does the transcript grow? How do sessions survive the process exiting?

model streamtokens, tool requests, thinking deltas

↓

event streamthe contract between layers

↓

agent loopdecide, call tools, update transcript

↓

sessioninspectable JSONL history

frontendprint, Rich, or TUI

The core idea

Separate the brain, the environment, and the face.

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.

02

What you can learn from Tau

Provider-neutral streaming interfaces

Agent loops that request and execute tools

Typed local tools for read, write, edit, and bash

Durable sessions under~/\.tau/sessions

Session resume, branching, JSONL export, and HTML export

Project instructions, skills, and prompt templates

Slash commands and model/provider selection

Context accounting, compaction, and thinking controls

How to keep Textual behind a UI adapter boundary

03

Educational principles

Small layers beat magic

One job per package. Study the provider layer, harness, and coding app on their own.

Events make agents teachable

The agent emits a stream you can render, test, and export — not control flow buried in callbacks.

Real enough to matter

Educational, not a toy. Run it as a real terminal agent while reading the code behind it.

Docs follow implementation

Built phase by phase, each with notes on what was added, why, and how it fits.

The inspiration

Inspired by Pi, written as a Python learning path.

Tau borrows Pi’s architectural lesson — keep the harness, the environment, and the UI apart. Not a line-by-line port; an educational Python take on the same core ideas.

τA map for building your own agent: start with events, add a loop, wrap it in a harness, then give it tools and a UI.