Headless CLI Agents

Headless CLI Agents

Build agentic systems using Claude Code CLI or the Claude Agent SDK.

CLI Headless Mode

Use -p flag for non-interactive execution:

# Basic query
claude -p "Explain this code"

# With JSON output for parsing
claude -p "Create a REST API" --output-format json

# Streaming JSON for real-time output
claude -p "Build a CLI app" --output-format stream-json

# Restrict tools
claude -p "Stage changes" --allowedTools "Bash,Read" --permission-mode acceptEdits

Output Formats

JSON response includes: session_id, total_cost_usd, duration_ms, num_turns, result.

Multi-Turn Sessions

# Get session ID
session_id=$(claude -p "Start review" --output-format json | jq -r '.session_id')

# Continue conversation
claude -p --resume "$session_id" "Now implement the plan"

# Or continue most recent
claude --continue "Add tests"

Key Flags

Python Agent SDK

pip install claude-agent-sdk

Basic Usage

import anyio
from claude_agent_sdk import query

async def main():
    async for message in query(prompt="What is 2 + 2?"):
        print(message)

anyio.run(main)

Custom Tools (In-Process MCP)

from claude_agent_sdk import tool, create_sdk_mcp_server, ClaudeSDKClient

@tool("greet", "Greet a user", {"name": str})
async def greet_user(args):
    return {"content": [{"type": "text", "text": f"Hello, {args['name']}!"}]}

server = create_sdk_mcp_server(name="my-tools", version="1.0.0", tools=[greet_user])
client = ClaudeSDKClient(mcp_servers=[server])

ClaudeSDKClient Options

from claude_agent_sdk import ClaudeSDKClient, ClaudeAgentOptions

options = ClaudeAgentOptions(
    system_prompt="You are a helpful assistant",
    working_directory="/path/to/project",
    allowed_tools=["Bash", "Read", "Write"],
    permission_mode="acceptEdits"
)

client = ClaudeSDKClient(options=options)

Agent Loop Pattern

Agents follow a core feedback loop:

1. Gather Context - Read files, search, web fetch
2. Take Action - Execute tools, generate code
3. Verify Work - Evaluate output, iterate if needed

Subagents

Use subagents for parallel execution with isolated context. Each subagent has its own context window and returns only relevant data to parent.

Best Practices

• Use JSON output for reliable parsing
• Check exit codes and stderr for errors
• Implement timeouts: timeout 300 claude -p "$prompt"
• Use session management for multi-step workflows
• Parse costs: echo "$result" | jq -r '.total_cost_usd'

Integration Examples

CI/CD Pipeline

#!/bin/bash
result=$(claude -p "Review PR diff for security issues" \
    --output-format json \
    --allowedTools "Read,Grep,WebSearch")

if echo "$result" | jq -e '.result | contains("vulnerability")' > /dev/null; then
    echo "Security issues found"
    exit 1
fi

Multi-Step Workflow

# Step 1: Plan
plan_result=$(claude -p "Create implementation plan for: $TASK" --output-format json)
session_id=$(echo "$plan_result" | jq -r '.session_id')

# Step 2: Implement
claude -p --resume "$session_id" "Implement the plan"

# Step 3: Test
claude -p --resume "$session_id" "Write tests for the implementation"

Rust CLI Integration

use std::process::Command;

async fn call_claude(prompt: &str) -> Result<String> {
    let output = Command::new("claude")
        .args(["-p", prompt, "--output-format", "json"])
        .output()?;

    let response: serde_json::Value = serde_json::from_slice(&output.stdout)?;
    Ok(response["result"].as_str().unwrap_or("").to_string())
}

References

• Headless Mode Docs
• Agent SDK Overview
• Claude Agent SDK Python