Glossary

Agent

A coding agent that a user runs inside T3 Code, such as Claude Code or Codex. T3 Code’s AGENTS.md notes that “agent” can also mean the AI that is changing the T3 Code repo itself.

Provider

The agent runtime that T3 Code talks to, such as Codex, Claude, Cursor, or OpenCode. Each provider has its own protocol, and T3 Code reaches it through an adapter.

Client

A user interface that connects to a T3 Code server: the web app, the desktop app, or the mobile app. The desktop app can also host a server.

Environment

One running T3 Code server, together with the machine, files, provider credentials, and saved state it owns. A client can connect to several environments at once, for example a laptop and a remote dev box.

Project

A record on one environment that points at a folder on that machine. Threads belong to a project.

Thread

The saved conversation and work history for a project. A thread survives when the provider process exits, so you can stop and resume it later.

Turn

One cycle where the user sends a message and the agent works on it, including follow-up work such as saving a checkpoint. The provider can finish before the follow-up work does.

T3 home

The base folder where T3 Code keeps its data, ~/.t3 by default. The live database sits under its userdata folder, which is why T3 Code’s agent guide tells contributors never to start a dev server against ~/.t3/userdata.

Monorepo

One Git repository that holds several apps and libraries that are built and versioned together. T3 Code keeps its server, web, desktop, and mobile apps and about thirty shared packages in one repo.

Workspace package

A folder inside a monorepo that has its own package.json and is listed in the workspace config, such as pnpm-workspace.yaml. Other packages depend on it with a workspace:* version instead of a version from the npm registry.

Barrel file

An index.ts file that re-exports everything in a package, so callers write one short import. Importing from a barrel loads every module it re-exports, which is why some T3 Code packages have no root export.

Subpath export

An entry in a package’s exports field that exposes one file under its own import path, such as @t3tools/shared/git. Callers import only the module they need.

Contract

The agreed shape of data that crosses a boundary, such as a request from a client to the server. In T3 Code the contracts live in packages/contracts, so the server and every client compile against the same types.

Schema

A value in code that describes a data shape and can check real data against it. T3 Code writes schemas with Effect’s Schema module. Zod is a similar library that you may know from your own projects.

WebSocket

A long-lived, two-way connection between a browser or app and a server. T3 Code clients send typed requests to a server and receive live updates over a WebSocket.

Effect

A TypeScript library for writing programs whose type records what they return, how they can fail, and what services they need. T3 Code’s server and scripts are written with it.

Service

In Effect, a named interface that a program asks for instead of importing a concrete implementation. T3 Code’s Effect services guide puts every server feature in a service, so WebSocket handlers, MCP tools, and scheduled tasks all call the same code.

Layer

In Effect, a recipe that builds a service, along with whatever that service needs. Tests swap in a different layer to replace a real dependency.

Typed error

An error whose possible kinds appear in a function’s type, so the compiler makes you handle each one. In T3 Code these are classes built with Schema.TaggedError, and callers handle them by tag.

Adapter

Code that translates between one outside system’s protocol and the shape your app uses inside. T3 Code has one adapter per provider, so the rest of the server works with one set of events.

MCP

Model Context Protocol, a standard way for an AI agent to discover and call tools that a server offers. T3 Code runs an MCP server so agents can create threads, read state, and drive the app.

Relay

A hosted service that helps clients find and connect to environments that are not on the same network. T3 Code’s relay lives in infra/relay and runs as a Cloudflare Worker.

T3 Connect

T3 Code’s own remote-access option. You sign in, and the relay gives your environment a tunnel so a phone or another computer can reach it without port forwarding.

Tailscale

A product that puts your devices on one private network, called a tailnet, wherever they are. T3 Code can use it as one route to a remote environment.

Electron

A framework that packages a web app with a copy of Chromium and Node.js as a desktop app. T3 Code’s desktop app is built on Electron and also bundles the server.

React Native

A framework for building iOS and Android apps with React components that render to native views. T3 Code’s mobile app uses it.

Lint rule

An automatic check that reads your source code and reports a pattern you have decided is a mistake. T3 Code writes its own rules when a review comment keeps repeating.

oxlint

A fast JavaScript and TypeScript linter written in Rust, part of the Oxc project. T3 Code runs it through vp lint and adds rules through a local plugin.

knip

A tool that finds unused files, unused dependencies, and unused exports in a JavaScript or TypeScript project.

vite-plus

A toolchain from VoidZero, the company behind Vite, that puts install, task running, linting, formatting, testing, and building behind one command, vp. T3 Code configures all of it from one root vite.config.ts.

Task cache

A record of a task’s inputs and output that lets a task runner skip the task when the inputs have not changed. vp run --cache keeps one, and T3 Code shares it between machines through a remote cache.

CI

Continuous integration, a server that runs checks such as tests and lint on every push or pull request. T3 Code runs CI on GitHub Actions.

Pull request

A request to merge one branch into another, with a page where people and bots review the change. On GitHub it is called a pull request, often shortened to PR.

Worktree

A second working folder for the same Git repository, created with git worktree add, that has its own branch checked out. T3 Code can run each thread in its own worktree, so several agents can work at once without touching each other’s files.

Orchestration

The part of T3 Code’s server that turns requests into commands, decides what events they produce, saves them, and then runs the side effects. It lives in apps/server/src/orchestration-v2.

Checkpoint

A saved snapshot of the project folder at the end of a turn. T3 Code stores it as a hidden Git ref, so it can show a diff or restore files without adding commits to your branch.

Agent skill

A folder with a SKILL.md file that teaches an agent one task, such as testing the app in a browser. T3 Code keeps its skills in .agents/skills.

Regression

A bug where something that used to work stops working after a change.

Scenario

In T3 Code, an end-to-end test that shows one behavior in the real app, with a real server and a real browser or simulator. A scenario is the proof for a bug fix, because it fails on the old commit and passes on the fix.

Eval

A test that runs a real AI model against real prompts or tool descriptions and scores what the model does. T3 Code uses evals in evals/ where a unit test cannot help, because model output changes from run to run.