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

Goes well beyond the annotations by disclosing the delivery contract: HMAC-SHA256 signing with the X-SimianX-Signature header, automatic retries, default-all event selection, and that the secret is shown only once. These are exactly the behavioral facts an agent cannot infer from readOnlyHint/openWorldHint/idempotentHint, and nothing contradicts the annotations.

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

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

Two short sentences, front-loaded with the core delivery behavior and followed by the routing hint. No filler, and the most decision-relevant clause (don't use this if you read get_updates) lands last for emphasis.

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

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

For a three-parameter creation tool with no output schema, the description covers delivery mechanics, auth/signing, retries, and usage scope. It omits only secondary details such as whether a webhook limit exists or what the creation response returns, which are minor given the annotation coverage.

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

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

Schema coverage is 100%, so all three parameters are already documented in the input schema, including 'default all' for events and 'shown once' for secret. The description echoes the events filtering ('or the kinds listed') but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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

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

The description states a concrete behavior: it POSTs updates to a URL, with a signature scheme and retries, and names itself as the webhook-creation path implicitly through the delivery semantics. It clearly separates itself from get_updates by declaring that tool unnecessary for agents. It never literally says 'creates a webhook', but the intent is unambiguous in context.

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

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

Provides a rare explicit when-not: 'an agent that reads get_updates does not need one' and scopes the tool to 'the user's own code'. It does not mention related siblings (list_webhooks, test_webhook, webhooks_update, delete_webhook) that an agent might need before or after creation, but the exclusions it does give are crisp.

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