Urlbox

Create a webhook endpoint

create_webhook

Destructive

Add a webhook endpoint to a project, so Urlbox POSTs render results to your URL when renders finish. Returns the endpoint's id. Its signing secret is not returned: the result explains how the user can get one without pasting it into the chat.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "intent": "<intent>",
      "url": "<url>"
    },
    "name": "create_webhook"
  }
}

Input Schema

Name	Required	Description
`url`	Yes	The HTTPS URL that receives render notifications.
`events`	No	Events to send. Defaults to every render event.
`intent`	Yes	Required. In one or two sentences, what you are trying to achieve for the user with this call and why (for example: 'Screenshot the pricing page so the user can compare plans'). Recorded for analytics and audit; do not include secrets.
`enabled`	No	Defaults to true.
`firesOn`	No	Fire for renders requested with these HTTP methods. Defaults to all.
`project`	No	Project id (proj_…) or exact name. Defaults to your default project.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 6, 2026

TDQS

A3.5/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety profile is covered by structured data. The description adds genuinely useful non-schema behavior: it returns only the endpoint id and deliberately withholds the signing secret, pointing the user to a safe retrieval path. It does not reiterate that the call creates persistent state or discuss rate limits, but the secret-handling detail is real added value.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences ordered by importance: what it does, what it returns, and the secret caveat. No filler, though the final clause ('without pasting it into the chat') is slightly conversational and could be tighter.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully discloses the return shape (an id) and the deliberately omitted secret. Against a 6-parameter creation tool with full annotation coverage, that is close to sufficient; only explicit guidance on side effects and prerequisites is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and every parameter carries its own documentation, including defaults and the audit-oriented 'intent' field. The description adds no parameter-level meaning beyond what the schema states, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Add a webhook endpoint to a project') plus the downstream effect ('Urlbox POSTs render results to your URL when renders finish'). The verb distinguishes it from the only close sibling, list_webhooks, though no sibling is named explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives context (webhooks fire on completed renders) but never says when to prefer this over alternatives or what prerequisites apply (e.g. permissions, project selection, whether a webhook already exists). Usage is implied rather than prescribed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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