pico

A Python CLI coding agent — autonomous, tool-using, and session-persistent. Inspired by Pi's modular, plugin-driven architecture.

pico operates on a repository on your behalf: reading, writing, and editing files, and running bash commands to build, test, and inspect the code. It runs in yolo mode (acts on its own without per-step approval), keeps an append-only, branchable session history, and automatically compacts context to stay within the model's token budget.

pico_ai ─► pico_core ─► pico_sdk ─► pico_tui
 (LLM)      (agent        (library      (terminal UI)
            loop/session)  API)

Features

• Headless CLI — picoCLI run "do a task" completes a coding task end-to-end with a single prompt.
• Interactive TUI — picoCLI-chat is a full terminal UI (Textual + Rich) for back-and-forth sessions.
• Status bar — the bottom bar always shows provider | model, a thinking indicator while streaming, and a color-coded context-window bar (green < 70%, yellow < 90%, red ≥ 90%) with the live token estimate.
• Nine hardcoded core tools — read, write, edit, grep, fetch, websearch, bash, todo, and task (see ADR-0003, ADR-0005).
• Todo tracking — the agent tracks multi-step work with a todo tool (add / update / list / clear); the TUI shows the in-memory list in a read-only side panel that appears once the first todo exists. A run only ends once every todo is completed — stopping early nudges the agent back in. When the run ends clean, the list is cleared for the next run (a run stopped by the stuck-model guard keeps its open todos).
• Sub-agents — the model delegates self-contained work via the task tool; each child runs isolated with its own session file, fresh todos, and restricted tools (overridable per spawn, never escalating past the parent), returning only a summary. Pure-delegation turns fan out in parallel; nesting is bounded (see ADR-0005).
• One-way LLM gateway — every provider is reached through one unified streaming "AI call" shape. Responses stream token-by-token.
• Six native providers — OpenRouter, OpenAI, Anthropic, Gemini, DeepSeek, and local Ollama, each a one-file adapter (pico_ai/providers/) normalizing to the same event shape. Switch with /provider (picker + per-provider setup form for API key, URL, model) or --provider (see ADR-0004).
• Reasoning & usage — thinking blocks stream live, then collapse to one clickable line (click to expand); token counts are estimated continuously for the status bar and compaction.
• Filterable pickers — /history, /model, /provider, and /skills all open modal pickers with a filter bar: type to narrow (case-insensitive substring), ↑/↓ to move, Enter to pick, Esc to cancel.
• Session tree — sessions are persisted as append-only trees of nodes; you can resume, rewind, and fork branches.
• Auto-compaction — context is summarised automatically at a token threshold, plus a manual override.
• Curated extensions — observe-only hooks (session_start, pre_tool_use, post_tool_use, post_tool_failure) and model-invoked SKILL.md skills from ~/.pico/skills/ + ~/.agents/skills/; permission gating via allowed_tools (see ADR-0003).
• Yolo mode — no approval prompts: it self-corrects by looping between streaming and tool execution.

Packages

Package	Responsibility	ADR
pico_ai	LLM abstraction; unified "AI call" + per-provider adapters	ADR-0001, ADR-0004
pico_core	The finite-state-machine agent loop + append-only session tree	ADR-0001, ADR-0002
pico_sdk	The headless AgentSession API + curated hooks/skills	ADR-0001, ADR-0003
pico_tui	The interactive terminal UI (Textual + Rich)	ADR-0001

Dependencies flow one way — pico_ai ← pico_core ← pico_sdk ← pico_tui (see ADR-0001). Sessions are a tree of immutable, append-only nodes (see ADR-0002).

Requirements

• Python 3.12+
• uv (workspace + dev tooling)
• An API key for your provider (or a local Ollama server — no key needed)

Providers

Provider	Default env var	Notes
OpenRouter (default)	OPENROUTER_API_KEY	Many models through one gateway; openrouter/free auto-resolves
OpenAI	OPENAI_API_KEY	GPT models
Anthropic	ANTHROPIC_API_KEY	Claude models; model list is curated (/model <id> for newer ones)
Gemini	GOOGLE_API_KEY	Google AI Studio
DeepSeek	DEEPSEEK_API_KEY	Chat + reasoner (reasoning streams as thinking blocks)
Ollama	—	Local server (OLLAMA_HOST, default http://localhost:11434)

In the TUI, /provider opens a picker with ✓/✗ setup status, then a setup form for that provider's API key, base URL, model, and extras. Only changed values are stored (in settings.json — prefer env vars on shared machines); blanks fall back to env/defaults. Effective precedence: field default < environment < stored value. Switching providers resets the model to that provider's stored/default model. Headless: picoCLI run --provider ollama "...".

Installation

uv sync

Configuration

1. Set your API key

The CLI reads the key from an environment variable (default OPENROUTER_API_KEY):

# temporary (current shell)
$env:OPENROUTER_API_KEY = "sk-or-v1-..."

# persistent (Windows, survives new shells)
setx OPENROUTER_API_KEY "sk-or-v1-..."

2. Optional settings.json

Create ~/.pico/settings.json to override defaults:

{
  "model": "openrouter/free",
  "context_window": 128000,
  "reserve_tokens": 16384,
  "session_dir": "~/.pico/sessions",
  "api_key_env": "OPENROUTER_API_KEY",
  "provider": "openrouter",
  "providers": {},
  "skills_dir": "~/.pico/skills",
  "allowed_tools": null
}

provider is the active backend id; providers holds per-provider stored values (e.g. {"openai": {"api_key": "sk-..."}}) — only changed form values are stored, blanks fall back to env/defaults. openrouter/free is an alias: at startup it resolves to the first alphabetically-sorted free model with tool support.

Usage

Headless runs

# complete a task in one shot
uv run picoCLI run "explain what this repo does"

# let the agent run shell commands (bash is on by default)
uv run picoCLI run "run the tests and fix failures"

# work in another directory, pick a model
uv run picoCLI run "summarize this code" --cwd D:\some\repo --model openai/gpt-4o-mini

# resume a previous session by id
uv run picoCLI run "continue" --session <session-id>

# compact a session headlessly (with optional steering text)
uv run picoCLI run "/compact focus on the auth refactor"

Flags for picoCLI run:

Flag	Purpose
--no-bash	Disable unsandboxed bash execution (on by default; ignored when allowed_tools is set without bash)
--provider <id>	Provider id (openrouter, openai, anthropic, gemini, deepseek, ollama)
--allow-tools <csv>	Tool allowlist, e.g. --allow-tools read,grep,bash (overrides settings.allowed_tools)
--skills-dir <path>	Override the configured skills directory
--no-skills	Disable SKILL.md loading
--model <name>	Override the configured model
--cwd <path>	Set the working directory
--session <id>	Resume an existing session

Interactive TUI

uv run picoCLI-chat

picoCLI-chat shares the same flags. Inside the prompt you can type a message or use:

Slash command	Key	Action
/help	F1	Show help
/history	Ctrl+H	Browse session nodes — pick one to jump to (forks the session)
/compact [text]	Ctrl+K	Compact context (optionally with steering text)
/model [name]	—	Change model (/model alone opens the interactive model picker; persists to settings.json)
/skills	—	Pick a loaded SKILL.md skill — inserts it into the input bar
/provider [id]	—	Pick the LLM provider, then fill its setup form (key, URL, model)
/fork <n or id>	—	Rewind to a node and start a new branch
/undo	Ctrl+Z	Rewind to the previous user turn
/quit	Ctrl+Q	Save the session and exit (/exit, /q also work)

Every picker has a filter bar at the top — typing narrows the list; Enter picks the highlighted row. Tool activity is rendered inline — bash commands echoed before running (green), and tool calls/results shown as color-coded panels (read blue, write yellow, edit magenta, bash green, todo cyan). todo calls stay hidden (only the todo result shows); thinking blocks stream in full then collapse to one 💭 thinking: … line, and bash results collapse to a one-line success/error — click either to expand. Failed tool calls (denied, unknown, or errored) render with a red border so permission gating is visible. The agent's todos also appear in a read-only panel on the right side of the chat while any exist.

Skills & permissions

Skills are model-invoked SKILL.md files — knowledge only, no code execution. Each skill is a directory with a SKILL.md (optional name/description frontmatter + markdown instructions):

~/.pico/skills/commit-helper/SKILL.md      # global
~/.agents/skills/commit-helper/SKILL.md    # shared (e.g. opencode/Matt Pocock), also loaded
<project>/.pico/skills/commit-helper/SKILL.md  # project-local, wins on name conflicts

---
name: commit-helper
description: Use when the user wants to commit code.
---
Run `git status` first, then ...

All discovered skills (alphabetical, no cap) are inlined into the system prompt. List them with /skills in the TUI, or disable with --no-skills / --skills-dir <path>.

Permission gating via allowed_tools in settings.json (null = all tools, [] = none) or --allow-tools read,grep,bash. Denied tools return an error: tool not allowed result the model can react to. When allowed_tools is set it wins over --no-bash; otherwise --no-bash disables bash.

Where sessions live

Sessions are persisted as JSONL under ~/.pico/sessions/<id>.jsonl by default (configurable via session_dir). Both picoCLI run and picoCLI-chat accept --session <id> to resume; /history, /fork, and /undo rewind within the tree without deleting nodes.

Development

# run all tests
uv run pytest

# typecheck every package
uv run mypy packages/pico_ai/src packages/pico_core/src packages/pico_sdk/src packages/pico_tui/src src/pico

# build all wheels into dist/ (root `pico-cli` is a meta-package: deps + entry points only)
uv build --package pico-cli --out-dir dist
uv build --package pico-ai --out-dir dist
uv build --package pico-core --out-dir dist
uv build --package pico-cli-sdk --out-dir dist
uv build --package pico-tui --out-dir dist

The test suite is network-free: it drives the whole agent loop through a scripted fake provider (FakeProvider) and a temporary filesystem, exercising pico_ai, pico_core, pico_sdk, and pico_tui.

Domain vocabulary

See CONTEXT.md for the full glossary. Key terms: session, node, payload, branch, fork, turn, tool / tool request / tool result, sub-agent, compaction, context window, provider, AI call, hook, skill.

Documentation

• Domain guide for agents
• Architecture decision records
• Issue-tracker conventions
• Milestone specs: headless agent, terminal UI