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This tutorial walks through the code-review-bot example from the SDK repository. By the end, you’ll understand how to combine custom tools, system prompts, completion lifecycle, and event streaming into a real application.

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What It Builds

A code review agent that:
  1. Reads a git diff from the local repo
  2. Optionally reads full file contents for context
  3. Produces structured review comments with severity levels
  4. Ends the run with a summary and approve/reject decision

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Prerequisites

  • Node.js 22+
  • An Anthropic API key
  • A git repository with at least one commit

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Get the Code

git clone https://github.com/cline/cline.git
cd cline/apps/examples/code-review-bot
bun install
Or read along with the source on GitHub.

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How It Works

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Defining Tools with Zod Schemas

The bot uses createTool with zod schemas for type-safe tool definitions. Here’s the review comment tool: 
createTool({
  name: "add_review_comment",
  description: "Add a review comment on a specific file and line.",
  inputSchema: z.object({
    file: z.string().describe("File path"),
    line: z.number().describe("Line number (approximate is fine)"),
    severity: z.enum(["critical", "warning", "suggestion"]),
    comment: z.string().describe("The review comment"),
  }),
  async execute(input) {
    reviews.push(input)
    return `Comment added (${reviews.length} total)`
  },
})
Key points:
  • z.enum constrains severity to valid values, which improves model accuracy
  • .describe() on each field tells the model what to provide
  • The tool accumulates results in an array for post-run processing

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Completion Tools

The submit_review tool uses lifecycle: { completesRun: true } to signal that the agent’s work is done: 
createTool({
  name: "submit_review",
  description: "Submit the completed review with a summary.",
  inputSchema: z.object({
    summary: z.string().describe("Brief overall assessment of the changes"),
    approve: z.boolean().describe("Whether the changes look good to merge"),
  }),
  lifecycle: { completesRun: true },
  async execute(input) {
    return JSON.stringify({ summary: input.summary, approve: input.approve })
  },
})
Without this, the agent would keep looping until maxIterations. With it, the agent calls submit_review when it’s done and the run ends cleanly.

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System Prompt

The system prompt gives the agent a structured workflow to follow: 
const agent = new Agent({
  systemPrompt: `You are a senior code reviewer. Analyze the git diff provided and leave review comments using the add_review_comment tool. Focus on:
- Bugs and logic errors (critical)
- Security issues (critical)
- Performance problems (warning)
- Style and readability improvements (suggestion)

When you are done reviewing, call submit_review with a brief summary.`,
  // ...
})
Telling the agent exactly which tools to use and when keeps the workflow predictable.

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Event Streaming

The bot subscribes to events to show progress as the agent works: 
agent.subscribe((event) => {
  switch (event.type) {
    case "assistant-text-delta":
      process.stdout.write(event.text ?? "")
      break
    case "tool-started":
      if (event.toolCall.toolName === "add_review_comment") {
        const input = event.toolCall.input
        console.log(`  [${input.severity}] ${input.file}:${input.line} - ${input.comment}`)
      }
      break
  }
})
This prints review comments as they’re made, so you see results streaming rather than waiting for the full run to finish.

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Post-Run Processing

After the run, the bot groups comments by severity and prints a summary: 
const result = await agent.run(`Review this git diff:\n\n\`\`\`diff\n${diff}\n\`\`\``)

const critical = reviews.filter((r) => r.severity === "critical")
const warnings = reviews.filter((r) => r.severity === "warning")
const suggestions = reviews.filter((r) => r.severity === "suggestion")
The tool calls accumulate structured data during the run, and the application processes it after. This pattern is useful any time you want the agent to produce structured output.

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Run It

ANTHROPIC_API_KEY=sk-ant-... bun dev        # review last commit
ANTHROPIC_API_KEY=sk-ant-... bun dev main   # review against main

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Extending Further

From here, you could:
  • Add a tool that posts review comments back to GitHub via the API
  • Use continue() for follow-up questions about specific findings
  • Add a checkstyle tool that runs linters on the changed files
  • Connect it to a webhook for automatic PR reviews

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More Examples

CLI Agent

Interactive terminal chat with tools and multi-turn conversation.

Multi-Agent

Parallel agents streaming to a web UI.
See Creating Custom Tools and Writing Plugins for more on extending agent capabilities.