ex_pi

ex_pi is an Elixir umbrella implementation of a pi-style AI coding agent. It combines a Phoenix LiveView chat UI, per-session BEAM processes, streaming LLM providers, JSONL session persistence, and a small coding-tool runtime.

The original TypeScript pi source is vendored at ./source for behavior checks while porting.

Applications

App	Module prefix	Role
ex_pi_ai	PiAi	Provider abstraction and Anthropic/OpenAI streaming parsers
ex_pi_agent	PiAgent	GenServer session loop, message transforms, compaction, tool calls
ex_pi_session	PiSession	Config, repository list, context-file assembly, JSONL replay/persistence
ex_pi_coding	PiCoding	Tool behaviour, dispatcher, permissions, read/write/edit/bash/search tools
ex_pi_web	PiWeb	Phoenix LiveView UI, routes, session process management

Features

• Phoenix LiveView UI for repositories, sessions, settings, and interactive permission prompts.
• Streaming Anthropic and OpenAI-compatible chat providers.
• Append-only JSONL session logs with replay, compaction entries, and session forking.
• Context-file assembly from AGENTS.md/CLAUDE.md, ordered from filesystem root to the active workdir.
• Coding tools for file reads, writes, edits, shell commands, glob/grep/ls, and URL fetches.
• DuskMoon UI components via phoenix_duskmoon.

Requirements

• Elixir ~> 1.18
• Erlang/OTP 27 or compatible with the configured Elixir version
• API credentials for Anthropic or an OpenAI-compatible provider

Setup

mix deps.get
mix assets.setup
mix phx.server

Open http://localhost:4580.

Provider settings are managed in the UI under /settings/providers and are saved in pi-compatible files under ~/.pi/agent/:

• settings.json
• auth.json
• models.json
• mcp.json
• AGENTS.md

Global MCP servers are configured under /settings/mcp. Project settings select the default MCP servers for that repository, and new sessions can override that selection.

Direct provider calls can also read environment fallbacks, but the LiveView flow resolves credentials from the saved settings above:

• Anthropic: ANTHROPIC_AUTH_TOKEN, optional ANTHROPIC_BASE_URL
• OpenAI-compatible: OPENAI_API_KEY or OPENROUTER_API_KEY, optional OPENAI_BASE_URL

Usage

1. Add a repository from the home page or visit /repository/new.
2. Open the repository session list.
3. Create or open a session.
4. Prompt the agent; tool calls stream back through LiveView and may request approval depending on policy.
5. Fork a session when you want a new branch of the same conversation history.

Repository routes use a Base64 URL-encoded absolute path without padding:

/repository/:repository
/repository/:repository/settings
/repository/:repository/sessions/:id

In development, repository and session state is stored locally:

• Repository list: apps/ex_pi_session/priv/repos.jsonl
• Session logs: apps/ex_pi_web/priv/sessions/<base64-url-workdir>/<session-id>.jsonl

Development

mix test
mix test apps/ex_pi_agent/test/ex_pi_agent_test.exs
mix test apps/ex_pi_agent/test/ex_pi_agent_test.exs:42
mix format --check-formatted
mix compile --warnings-as-errors
mix assets.build

The web app uses DuskMoon UI. Keep UI work on phoenix_duskmoon components and the configured Tailwind/DuskMoon pipeline; do not add DaisyUI or Phoenix core_components.ex.

License

This project follows the licensing terms of the upstream pi project unless stated otherwise.