Custom Tools

Custom tools extend what your AI can do. Describe what you need in plain language, your AI builds it, you review and approve it, then it becomes a tool your AI can use in any conversation.

How It Works

1. Describe — Tell your AI what you need: "build me a tool that creates GitHub issues"
2. AI builds — Your AI generates the tool definition and code
3. It's live — The tool is active immediately and available in every conversation
4. Configure — Choose visibility, scheduling, email triggers, and more

All custom tool operations use the tool tool with an action parameter.

Tool Types

Quick Examples

Service Connector (http_proxy)

Connect to any API with templated requests:

tool(action="create",
  name="github_create_issue",
  description="Create an issue in a GitHub repository",
  tool_type="http_proxy",
  input_schema={
    type: "object",
    properties: {
      owner: { type: "string" },
      repo: { type: "string" },
      title: { type: "string" }
    },
    required: ["owner", "repo", "title"]
  },
  http_config={
    method: "POST",
    url_template: "https://api.github.com/repos/{{owner}}/{{repo}}/issues",
    body_template: { title: "{{title}}" },
    connection_id: "my-github-connection"
  })

See Service Connectors for the full guide.

Data Transform (transform)

Reshape data with JSONata expressions:

tool(action="create",
  name="calculate_discount",
  description="Calculate discounted price",
  tool_type="transform",
  input_schema={
    type: "object",
    properties: {
      price: { type: "number" },
      discount_percent: { type: "number" }
    },
    required: ["price", "discount_percent"]
  },
  transform_config={
    expression: "input.price * (1 - input.discount_percent / 100)"
  })

See Data Transforms for the full guide.

Workflow Chain (chain)

Run multiple tools in sequence:

tool(action="create",
  name="deploy_and_notify",
  description="Deploy to production and notify the team",
  tool_type="chain",
  input_schema={
    type: "object",
    properties: {
      environment: { type: "string" },
      message: { type: "string" }
    },
    required: ["environment"]
  },
  chain_config={
    steps: [
      { tool_name: "cloudflare_deploy", input_mapping: { env: "{{environment}}" } },
      { tool_name: "slack_notify", input_mapping: { channel: "#deploys", text: "Deployed to {{environment}}: {{message}}" } }
    ]
  })

See Workflow Chains for the full guide.

Code Tool (code)

Run custom JavaScript in isolated containers:

tool(action="create",
  name="calculate_statistics",
  description="Calculate statistical measures for a list of numbers",
  tool_type="code",
  input_schema={
    type: "object",
    properties: {
      numbers: { type: "array", items: { type: "number" } }
    },
    required: ["numbers"]
  },
  code_config={
    code: "export default { async fetch(request) { const { numbers } = await request.json(); const mean = numbers.reduce((a, b) => a + b, 0) / numbers.length; return Response.json({ mean, count: numbers.length }); } }",
    runtime: "javascript",
    allowed_domains: []
  })

See Code Tools for the full guide.

Skill-Backed (skill_backed)

Tools powered by approved Kyew skills:

tool(action="create",
  name="weekly_report",
  description="Generate a weekly report from my memories",
  tool_type="skill_backed",
  skill_id="skill_abc123")

Managing Tools

List Your Tools

tool(action="list")
tool(action="list", status="active")
tool(action="list", tool_type="code")

Get Tool Details

tool(action="get", tool_id="tool_abc123")

Update a Tool

tool(action="update", tool_id="tool_abc123", description="Updated description", status="active")

Delete a Tool

tool(action="delete", tool_id="tool_abc123")

Test a Tool

tool(action="test", tool_id="tool_abc123", test_input={ numbers: [1, 2, 3] })

Tool Status

Tools are active by default when created.

Tool Visibility

Control whether a tool appears in your AI's tool list:

Toggle visibility anytime:

tool(action="update", tool_id="tool_abc123", visibility="unlisted")

See Tool Visibility for details.

Connections

Custom tools that call external APIs need credentials. Connections store API keys, OAuth tokens, and other credentials securely. Create a connection once, reference it in any number of tools.

Scheduling

Schedule code tools to run automatically at specific hours with optional email summaries.

Per-User Database

Code tools get access to a per-user SQLite database (10 GB) for persistent storage. See the Database Guide for patterns and usage.

API Reference

For the full technical reference including all parameters and options, see tool Tool Reference.