FemtoAgent: Minimal CLI AI Coding Assistant

A lightweight bash-based AI coding agent that uses the OpenRouter API with native tool calls.

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                         agent.sh                             │
│                   Tool-Call Based CLI Agent                     │
└─────────────────────────────────────────────────────────────────┘

    ┌──────────────────┐
    │   User Input     │
    │   "You: ___"     │
    └────────┬─────────┘
             │
             ▼
    ┌──────────────────────────────────────────────────┐
    │  Build context:                                  │
    │  • System prompt (cached)                        │
    │  • Conversation history (cached)                 │
    │  • <previous-result> + <task> tags               │
    └────────────────────┬─────────────────────────────┘
                         │
                         ▼
    ┌─────────────┐         ┌─────────────────┐
    │  agent   │──curl──▶│  OpenRouter API │
    │             │◀────────│  (Claude Model) │
    └─────────────┘         └─────────────────┘
                         │
           ┌─────────────┴─────────────┐
           ▼                           ▼
    ┌──────────────┐           ┌───────────────┐
    │  Tool Call   │           │  Text Reply   │
    │  run_script  │           │  (no tool)    │
    └──────┬───────┘           └───────────────┘
           │
           ▼
    ┌──────────────────┐
    │ Show script      │
    │ Ask "Run? (y/n)" │
    └────────┬─────────┘
             │ (confirmed)
             ▼
    ┌──────────────────────────────────────────────────┐
    │  bash -c "$script" ──┬──▶ stdout                 │
    │                      └──▶ result.txt (for next)  │
    └──────────────────────────────────────────────────┘

Files

├── agent.sh        # Main agent script
├── history.json       # Conversation memory [{role,content},...]
├── result.txt         # Last script output (fed back to AI)
└── system_prompt.txt  # Customizable system instructions

Usage

1. Set your OpenRouter API key:

export OPENROUTER_API_KEY="your-key"

2. Run the agent:

bash agent.sh

3. Describe tasks in plain English
4. Review and confirm script execution with y/n

Auto-execute mode

AUTO=1 bash agent.sh

Requirements

• curl
• jq
• coreutils

Configuration

Variable	Default	Description
OPENROUTER_API_KEY	(required)	Your OpenRouter API key
MODEL	anthropic/claude-sonnet-4-20250514	Model to use
ENDPOINT	https://openrouter.ai/api/v1/chat/completions	API endpoint
AUTO	0	Set to 1 to auto-execute scripts

How It Works

1. User describes a task in natural language
2. Agent builds messages with system prompt + history + current task
3. Sends request to OpenRouter with run_script tool definition
4. AI responds with either:
   • Tool call: Script to execute (user confirms, output saved)
   • Text: Direct response (displayed to user)
5. History and results persist for multi-turn conversations
6. Prompt caching reduces API costs on repeated context