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

Annotations only declare the generic non-read-only, non-destructive profile; the description adds the substantive behavior an agent needs: senders need no credentials by default, inspection always requires workspace credentials or the private token, visibility=private flips the sender requirement, and the inbox self-expires in an hour. It also discloses the plan ceiling on TTL, which is real operational context not present in annotations or schema.

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?

Front-loaded with the purpose, then ordered by what the agent must decide (credentials model, visibility, TTL, token handling, next tool). Dense sentences such as the expiry clause pack two facts together and the pronoun "It" briefly obscures its referent, but no sentence is filler.

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?

There is no output schema, and the description compensates by naming the two returned artifacts that matter: webhookUrl and the private inspection token that must be saved. For a zero-required-parameter creation tool with full schema coverage, nothing an agent needs to call it correctly is missing.

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 the baseline is 3, but the description adds genuine meaning: it explains the security consequence of visibility=private (sender must supply X-Access-Token) and supplies plan-dependent ttlSeconds maximums (1 hour anonymous, 7 days on Free) that the schema's "from 60" does not convey.

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?

Opens with a specific verb and resource: "Create a webhook receiver." Together with the webhookUrl and inspection-token language, an agent can distinguish this from sibling creators like create_email_inbox or create_mock_api without opening the schema.

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?

Gives clear operating context: public POST-by-default mode, private mode gated on X-Access-Token, one-hour default expiry, and an explicit next step ("use wait_for_webhook"). It does not explicitly contrast with other inbox types or state when not to create one, so it falls short of full alternative routing.

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