Build a tool

Build a tool when Find a tool turns up nothing for your task. A build explores the website, writes the tool, runs your example once and publishes it, in about 10 minutes. After that the tool runs in seconds.

Start a build

Describe the task, name the website and its effect, and give one example input.

{
  "name": "build_website_tool",
  "arguments": {
    "task": "Search Instacart for a product and return the top results with name, size and price.",
    "site_url": "https://www.instacart.com",
    "effect": "read",
    "example_input": "{\"query\":\"oat milk\"}",
    "idempotency_key": "build-oat-milk-search"
  }
}

Field	What to send
`task`	What the tool should do, in plain words
`site_url`	The website’s https address. Required; a path is ignored
`effect`	`read`, `write` or `ask`. See Choose an effect
`example_input`	The input for the one real example the build runs
`start_url`	Optional: the exact https page on the site to start from

Over REST, send the same fields to POST /v1/builds. On an integration MCP, build_tool does the same for that integration’s website and needs no site_url.

Follow the build

The call answers its job at once. Tell the person the tool is building, then wait for the job. A build may stop to ask a question, such as which login to use; see Answer a job’s questions. While it runs, the job’s build field shows its stage and an estimate.

When it ends

Published: the job succeeds with the new tool’s tool_id. See Check the example result.
Already covered: an existing tool does the task. The job succeeds with it as tool_id and build.existing_tool_id, and publishes nothing.
Blocked: the build found the task impossible on this site. It fails with build_blocked; show its message to the person.

Details

A build without a site_url, or with an address that isn’t a plain https origin, creates no job and answers invalid_request.
Builds for ticket, bank or government websites are refused with site_not_supported.
A published build counts toward your plan. See Plans and limits.
A new tool joins its website’s integration, named in build.integration_id. See Use integration MCPs.

Get started

Example guides

Guides

Start a build

Follow the build

When it ends

​Start a build

​Follow the build

​When it ends

Start a build

Follow the build

When it ends