---
title: "Invoke a discovered WebMCP tool"
method: POST
path: "/browsers/{id_or_name}/webmcp/invoke"
tags: ["Browser WebMCP"]
---

# Invoke a discovered WebMCP tool

`POST /browsers/{id_or_name}/webmcp/invoke`

## Request

- Base URL: `https://api.onkernel.com`
- URL: `https://api.onkernel.com/browsers/{id_or_name}/webmcp/invoke`
- Auth: HTTP bearer

Invokes the exact live registration identified by tool_ref. Non-autosubmit declarative form
tools return after their fields are populated with an awaiting_submission status. Other tools
wait for a terminal result, including across navigation. Inspect a populated form, obtain any
required confirmation, then submit through Playwright or computer interaction without invoking
the tool again. If the tab or embedded frame disappears, or the request times out after invocation
begins, the response reports outcome_unknown and the tool is not retried.
CDP-backed custom tool outputs above 240 KiB return an error rather than a truncated result.

## Path parameters

- `id_or_name` string, required

## Request body

- WebMCPInvokeRequest
  - `input` object, required: Tool input, limited to 1 MiB after JSON serialization.
  - `timeout_sec` integer
  - `tool_ref` string, required

## Response `200`

The populated non-autosubmit form state or the tool's terminal result

- WebMCPInvocationResult
  - `error_text` string
  - `invocation_id` string, required
  - `output` unknown
  - `status` 'completed' | 'canceled' | 'error' | 'awaiting_submission', required: awaiting_submission means a non-autosubmit declarative form was populated but not submitted. Inspect the form, obtain any required confirmation, then submit through Playwright or computer interaction without invoking the tool again. The other statuses are terminal results.

## Other responses

- `400`: Bad Request – invalid input
- `404`: Resource not found
- `500`: Internal Server Error
- `504`: Invocation began, but its final outcome could not be observed
- `default`: Error returned by the browser or its proxy

## Changes

- **2026-10-16** `03b369edee49`: 1 info
  - endpoint added

[Operation history](https://skmtc.dev/kernel/apis/kernel-api/changes/browsers/:id_or_name/webmcp/invoke/post.md)

---

[API](https://skmtc.dev/kernel/apis/kernel-api.md) - [All operations](https://skmtc.dev/kernel/apis/kernel-api/llms.txt) - [OpenAPI document](https://skmtc.dev/kernel/apis/kernel-api/revisions/0f6cf4f58fe6?raw)