ApeCode 🦧

A nano terminal code agent in Python — a minimal but complete implementation of a tool-calling AI agent (like Claude Code / Codex CLI / Kimi CLI), built for learning and experimentation.

Powered by ApeCode.ai

Features

• Tool-calling agent loop — user → model → tool calls → tool results → model → response, with configurable max-steps guard
• Multi-provider model adapters — OpenAI, Anthropic, and Kimi (OpenAI-compatible), all conforming to a unified ChatModel protocol
• 7 built-in tools — list_files, read_file, write_file, replace_in_file, grep_files, exec_command, update_plan
• Sandbox + approval model — SandboxMode (read-only / workspace-write / danger-full-access) restricts path mutations; ApprovalPolicy (on-request / always / never) controls interactive confirmation for mutating operations
• Plugin system — declarative apecode_plugin.json manifests contribute tools, slash commands, and skills
• MCP integration — load external tools from .mcp.json / apecode_mcp.json via the fastmcp SDK
• Slash commands — /help, /tools, /skills, /skill, /plan, /subagents, /delegate, /exit
• Subagent delegation — isolated read-only agents with three default profiles: general, reviewer, researcher
• Skill templates — discoverable from skills/*/SKILL.md directories or plugins
• REPL + one-shot mode — interactive session with prompt-toolkit (history, tab-completion, multi-line via Alt+Enter) or single-prompt execution
• Thinking model support — displays reasoning_content from thinking models (e.g. Kimi K2.5)
• AGENTS.md chain — walks from workspace root to filesystem root, loading AGENTS.md files for project-specific instructions

Installation

uv sync

Dependencies: openai, anthropic, fastmcp, typer, rich, prompt-toolkit.

Usage

API keys

export OPENAI_API_KEY=your_key       # for provider=openai (default)
export ANTHROPIC_API_KEY=your_key    # for provider=anthropic
export KIMI_API_KEY=your_key         # for provider=kimi

Interactive REPL

uv run ape

One-shot mode

uv run ape "read README.md and summarize project structure"

CLI flags

uv run ape --provider openai --model gpt-4.1-mini    # default
uv run ape --provider anthropic --model claude-sonnet-4-20250514
uv run ape --provider kimi --model kimi-k2.5
uv run ape --max-steps 30 --timeout 180
uv run ape --cwd /path/to/repo
uv run ape --sandbox-mode read-only --approval-policy never
uv run ape --plugin-dir ./plugins
uv run ape --mcp-config ./.mcp.json
uv run ape --skill-dir ./custom-skills
uv run ape --yolo "apply a simple refactor in src/"
uv run ape --version

Slash commands (inside REPL)

/help                                          — list all commands
/tools                                         — list registered tools
/skills                                        — list discovered skills
/skill concise-review review src/apecode/cli.py — run a skill with extra request
/plan                                          — show the current task plan
/subagents                                     — list subagent profiles
/delegate reviewer:: review src/apecode/cli.py — delegate to a subagent
/exit                                          — quit

Architecture

user input
    │
    ▼
┌──────────────────────────────────────────────┐
│  cli.py — Typer app, _build_runtime, REPL    │
│  ┌────────────────────────────────────────┐  │
│  │  NanoCodeAgent (agent.py)              │  │
│  │  ┌──────────┐    ┌──────────────────┐  │  │
│  │  │ ChatModel │◄──│ model_adapters.py │  │  │
│  │  │ protocol  │   │ OpenAI/Anthropic/ │  │  │
│  │  │           │   │ Kimi adapters     │  │  │
│  │  └──────────┘    └──────────────────┘  │  │
│  │  ┌──────────────────────────────────┐  │  │
│  │  │ ToolRegistry (tools.py)          │  │  │
│  │  │  7 built-in + plugin + MCP tools │  │  │
│  │  │  ToolContext: sandbox + approval  │  │  │
│  │  └──────────────────────────────────┘  │  │
│  └────────────────────────────────────────┘  │
│  commands.py — slash command registry        │
│  plugins.py  — apecode_plugin.json loader    │
│  mcp.py      — fastmcp stdio bridge          │
│  skills.py   — SKILL.md discovery + catalog  │
│  subagents.py — isolated read-only delegates │
│  system_prompt.py — prompt builder + AGENTS.md│
│  console.py  — Rich + prompt-toolkit I/O     │
└──────────────────────────────────────────────┘

Module breakdown

Module	Purpose
cli.py	Typer entry point, assembles runtime (_build_runtime), runs REPL or one-shot
agent.py	NanoCodeAgent — the core tool-calling loop with ChatModel protocol
tools.py	ToolRegistry, ToolContext (sandbox/approval), 7 built-in tool handlers
model_adapters.py	OpenAIChatCompletionsClient, AnthropicMessagesClient, KimiChatCompletionsClient — all adapters convert to/from internal OpenAI message format
commands.py	CommandRegistry + SlashCommand — /help, /tools, /exit, etc.
plugins.py	Loads apecode_plugin.json manifests; registers tools, commands, skills
mcp.py	Parses .mcp.json, connects via fastmcp.Client, registers MCP tools
skills.py	SkillCatalog — discovers SKILL.md files, supports plugin-contributed skills
subagents.py	SubagentRunner — spawns isolated agents with read-only tools and capped steps
system_prompt.py	Builds system prompt with environment info, AGENTS.md chain, skill catalog
console.py	Rich console output (panels, spinners, tool call display) + prompt-toolkit input session

Environment Variables

Variable	Default	Description
APECODE_PROVIDER	openai	Model provider (openai / anthropic / kimi)
APECODE_MODEL	gpt-4.1-mini	Model name
APECODE_SANDBOX_MODE	workspace-write	Sandbox mode (read-only / workspace-write / danger-full-access)
APECODE_APPROVAL_POLICY	on-request	Approval policy (on-request / always / never)
OPENAI_API_KEY	—	OpenAI API key
OPENAI_BASE_URL	https://api.openai.com/v1	Custom OpenAI-compatible endpoint
ANTHROPIC_API_KEY	—	Anthropic API key
ANTHROPIC_BASE_URL	https://api.anthropic.com/v1	Custom Anthropic endpoint
ANTHROPIC_API_VERSION	2023-06-01	Anthropic API version header
KIMI_API_KEY	—	Kimi API key
KIMI_BASE_URL	https://api.moonshot.cn/v1	Kimi endpoint

Plugin System

Place a plugin manifest as apecode_plugin.json in a plugin directory:

{
  "name": "EchoPlugin",
  "tools": [
    {
      "name": "echo_text",
      "description": "Echo text from JSON args",
      "parameters": {
        "type": "object",
        "properties": { "text": { "type": "string" } },
        "required": ["text"],
        "additionalProperties": false
      },
      "argv": ["python3", "/absolute/path/to/tool.py"],
      "mutating": false,
      "timeout_sec": 60
    }
  ],
  "commands": [
    {
      "name": "quick-review",
      "description": "Run plugin prompt template",
      "usage": "/quick-review <task>",
      "output": "Running quick review...",
      "agent_input_template": "Review this task:\\n{args}"
    }
  ],
  "skills": [
    {
      "name": "plugin-skill",
      "description": "A plugin-provided skill",
      "content": "# Plugin Skill\\n\\nKeep output concise."
    }
  ]
}

• Tools use either argv (recommended) or command to specify the executable.
• Tool processes receive JSON arguments on stdin and write results to stdout.
• Commands support {args} placeholder in agent_input_template.
• Skills can use inline content or a file path relative to the manifest.

MCP Config

Load MCP tools from .mcp.json or apecode_mcp.json in workspace root, or via --mcp-config:

{
  "mcpServers": {
    "demo": {
      "command": "python3",
      "args": ["/absolute/path/to/mcp_server.py"],
      "timeout_sec": 30
    }
  }
}

Skills

Create a skill as skills/<name>/SKILL.md:

# concise-review

Review code and answer with concise bullet points.

Use inside REPL:

/skill concise-review review src/apecode/agent.py

Development

# Install dev dependencies
uv sync

# Run tests
uv run pytest

# Run a single test file
uv run pytest tests/test_tools.py -v

# Lint
uv run ruff check src/ tests/

# Lint with auto-fix
uv run ruff check --fix src/ tests/

# Format
uv run ruff format src/ tests/

Project Structure

src/apecode/
├── __init__.py          # package version
├── __main__.py          # python -m apecode entry
├── cli.py               # Typer CLI app + runtime assembly
├── agent.py             # NanoCodeAgent core loop
├── tools.py             # tool registry + built-in tools
├── model_adapters.py    # model adapters (OpenAI/Anthropic/Kimi)
├── commands.py          # slash command framework
├── plugins.py           # plugin manifest loader
├── mcp.py               # MCP stdio bridge
├── skills.py            # skill discovery + catalog
├── subagents.py         # subagent delegation
├── system_prompt.py     # system prompt builder
└── console.py           # Rich + prompt-toolkit I/O
tests/
├── test_agent.py
├── test_commands.py
├── test_mcp.py
├── test_model_adapters.py
├── test_plugins.py
├── test_skills.py
├── test_subagents.py
└── test_tools.py

License

Apache-2.0