coding-agent-builder

Build custom branded coding agents using Claude Code's powerful harness and the Anthropic Agent SDK. Create your own AI coding assistant with your company's branding, specialized agents, custom commands, MCP integrations, and hooks.

Why This SDK?

Claude Code is a powerful AI coding assistant, but you can't customize its branding or extend it with domain-specific capabilities. This SDK gives you full access to Claude Code's infrastructure while letting you customize everything:

| Feature | What You Can Do | |---------|-----------------| | Branding | Custom name, colors, welcome message, prompts | | Agents | Specialized sub-agents (security, review, devops) | | Commands | Custom slash commands (/audit, /deploy) | | MCP Servers | Connect databases, APIs, custom tools | | Hooks | Intercept tool calls, add logging, enforce policies | | Tools | Use Claude Code's built-in tools or restrict them | | Permissions | Control what your agent can access |

Build Tools Like

• hawk - Security-focused code auditor
• devops-ai - Infrastructure and deployment assistant
• code-mentor - Onboarding tool for new developers
• db-assistant - Database query helper with MCP

Installation

bun add @franalgaba/coding-agent-builder

Quick Start

import { createCLI } from "@franalgaba/coding-agent-builder";

await createCLI({
  name: "hawk",

  agents: {
    "security-auditor": {
      description: "Audit code for security vulnerabilities",
      prompt: "You are a security expert...",
    },
  },

  commands: {
    audit: {
      description: "Run security audit",
      content: "Perform a security audit of this codebase.",
    },
  },
}).start();

Features

Custom Agents

Define specialized sub-agents that Claude can delegate to:

createCLI({
  agents: {
    "security-auditor": {
      description: "Use for security vulnerability scanning",
      prompt: `You are a security expert. When auditing:
        1. Check for OWASP Top 10 vulnerabilities
        2. Look for hardcoded secrets
        3. Review auth/authz patterns
        4. Identify injection risks`,
      model: "opus",  // Use stronger model for security
      tools: ["Read", "Grep", "Glob", "Bash"],
    },

    "perf-analyzer": {
      description: "Use for performance analysis",
      prompt: "You analyze code for performance issues...",
      model: "haiku",  // Fast model for quick analysis
      tools: ["Read", "Grep"],
    },
  },
});

Agent Options:

• description - When Claude should use this agent
• prompt - System prompt for the agent
• model - "sonnet", "opus", "haiku", or "inherit"
• tools - Allowed tools (restricts what agent can do)

Custom Commands

Create slash commands users can invoke:

createCLI({
  commands: {
    audit: {
      description: "Run security audit on codebase",
      content: `Perform a comprehensive security audit:
        1. Scan for vulnerabilities
        2. Check dependencies
        3. Review auth patterns
        4. Generate report`,
      argumentHint: "<directory>",
      allowedTools: ["Read", "Grep", "Glob", "Bash"],
    },

    review: {
      description: "Review current PR changes",
      content: "Review git diff and provide feedback on code quality.",
    },

    deploy: {
      description: "Help with deployment",
      content: "Guide through deployment process for this project.",
      allowedTools: ["Read", "Bash"],
    },
  },
});

Users can then run /audit src/ or /review in the CLI.

MCP Servers

Connect to external tools via Model Context Protocol:

createCLI({
  mcpServers: {
    // Stdio-based MCP server
    "postgres": {
      command: "npx",
      args: ["-y", "@modelcontextprotocol/server-postgres"],
      env: {
        DATABASE_URL: process.env.DATABASE_URL,
      },
    },

    // HTTP-based MCP server
    "internal-api": {
      type: "http",
      url: "https://api.internal.company.com/mcp",
      headers: {
        Authorization: `Bearer ${process.env.API_TOKEN}`,
      },
    },

    // SSE-based MCP server
    "realtime-data": {
      type: "sse",
      url: "https://stream.example.com/mcp",
    },
  },
});

MCP Server Types:

• stdio - Local process (default)
• http - HTTP endpoint
• sse - Server-Sent Events

Hooks

Intercept events for logging, policy enforcement, or custom behavior:

createCLI({
  hooks: {
    // Before any tool runs
    PreToolUse: [
      {
        matcher: "Bash",  // Only for Bash commands
        handler: async ({ toolName, toolInput }) => {
          console.log(`[AUDIT] Running: ${toolInput.command}`);

          // Block dangerous commands
          if (toolInput.command.includes("rm -rf /")) {
            return {
              decision: "block",
              message: "Dangerous command blocked"
            };
          }
          return { decision: "allow" };
        },
      },
    ],

    // After tool completes
    PostToolUse: [
      {
        handler: async ({ toolName, toolResult }) => {
          // Log all tool results
          await logToMonitoring({ toolName, result: toolResult });
        },
      },
    ],

    // Session lifecycle
    SessionStart: [
      {
        handler: async () => {
          console.log("Session started at", new Date());
        },
      },
    ],

    SessionEnd: [
      {
        handler: async ({ totalCost }) => {
          await reportUsage(totalCost);
        },
      },
    ],

    // User input
    UserPromptSubmit: [
      {
        handler: async ({ prompt }) => {
          // Filter or transform user input
          return { prompt: sanitize(prompt) };
        },
      },
    ],
  },
});

Hook Events:

• PreToolUse - Before tool execution (can block)
• PostToolUse - After tool execution
• SessionStart - When session begins
• SessionEnd - When session ends
• UserPromptSubmit - When user sends message
• Notification - System notifications
• Stop - When agent stops

Tools Configuration

Control which tools are available:

createCLI({
  // Use Claude Code's full toolset
  tools: { type: "preset", preset: "claude_code" },

  settings: {
    // Allow specific tools
    allowedTools: ["Read", "Write", "Edit", "Bash", "Grep", "Glob"],

    // Or block specific tools
    disallowedTools: ["WebFetch", "WebSearch"],
  },
});

Available Tools:

• Read, Write, Edit - File operations
• Bash - Shell commands
• Grep, Glob - Search
• WebFetch, WebSearch - Web access
• Task - Sub-agent spawning
• TodoWrite - Task tracking
• NotebookEdit - Jupyter notebooks
• Plus any MCP-provided tools

System Prompt

Customize the agent's base instructions:

createCLI({
  // Option 1: Extend Claude Code's prompt
  systemPrompt: {
    type: "preset",
    preset: "claude_code",
    append: `
      Additional instructions for your company:
      - Follow our coding standards at docs/standards.md
      - Always run tests before suggesting changes
      - Use our internal APIs when possible
    `,
  },

  // Option 2: Completely custom prompt
  systemPrompt: `You are a specialized coding assistant for Acme Corp...`,
});

Settings & Permissions

Fine-tune behavior:

createCLI({
  settings: {
    // Model selection
    model: "claude-sonnet-4-20250514",

    // Permission modes
    permissionMode: "auto",  // "auto" | "manual" | "none"

    // Limits
    maxTurns: 50,
    maxThinkingTokens: 10000,

    // Custom instructions (appended to system prompt)
    customInstructions: "Always explain your reasoning step by step.",
  },

  // Directories the agent can access
  additionalDirectories: [
    "/shared/company-libs",
    "/docs",
  ],

  // Session management
  session: {
    resume: "session-id-here",  // Resume previous session
    continue: true,              // Continue last session
  },
});

Custom TUI Mode

Full control over the terminal interface:

createCLI({
  mode: "tui",

  tui: {
    branding: {
      name: "Hawk",
      tagline: "AI Security Auditor",
      welcomeMessage: "Ready to audit your code. Type /help for commands.",
      promptPrefix: "hawk> ",
    },

    theme: {
      colors: {
        primary: "#F59E0B",   // Amber
        accent: "#3B82F6",    // Blue
        success: "#10B981",   // Green
        error: "#EF4444",     // Red
        muted: "#6B7280",     // Gray
      },
    },

    display: {
      showToolProgress: true,
      showThinking: true,
      showCost: true,
      truncateToolOutput: 500,
    },
  },
});

Full Example

import { createCLI } from "@franalgaba/coding-agent-builder";

await createCLI({
  name: "hawk",

  // Extend Claude Code's capabilities
  systemPrompt: {
    type: "preset",
    preset: "claude_code",
    append: "Focus on security best practices.",
  },

  // Specialized agents
  agents: {
    "vuln-scanner": {
      description: "Scan for security vulnerabilities",
      prompt: "You are an expert at finding security vulnerabilities...",
      tools: ["Read", "Grep", "Glob"],
    },
    "secrets-detector": {
      description: "Find exposed secrets and credentials",
      prompt: "You scan code for hardcoded secrets...",
      tools: ["Read", "Grep"],
    },
  },

  // Custom commands
  commands: {
    audit: {
      description: "Full security audit",
      content: "Perform comprehensive security audit.",
    },
    secrets: {
      description: "Scan for secrets",
      content: "Find any exposed secrets or credentials.",
    },
  },

  // MCP integrations
  mcpServers: {
    "snyk": {
      command: "npx",
      args: ["snyk-mcp-server"],
    },
  },

  // Hooks for audit logging
  hooks: {
    PreToolUse: [{
      handler: async ({ toolName, toolInput }) => {
        console.log(`[AUDIT] ${toolName}:`, toolInput);
        return { decision: "allow" };
      },
    }],
  },

  // Settings
  settings: {
    model: "claude-sonnet-4-20250514",
    permissionMode: "auto",
  },
}).start();

Two Modes

| Mode | Description | Use When | |------|-------------|----------| | tui (default) | Custom TUI with pi-tui framework | You want a branded, customizable interface | | spawn | Uses Claude Code's native TUI | You want full Claude Code experience |

// TUI mode (default) - Custom branded interface
createCLI({ name: "hawk", ... });

// Spawn mode - Claude Code's native TUI with your plugins
createCLI({ mode: "spawn", ... });

API Reference

createCLI(config: CLIConfig): CLI

Creates a new CLI instance.

CLI.start(): Promise<CLIResult>

Starts the interactive session.

CLI.interrupt(): void

Interrupts the current operation.

CLI.getSessionId(): string | null

Returns the current session ID.

Requirements

• Bun >= 1.0.0
• ANTHROPIC_API_KEY environment variable

License

MIT