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

Annotations only declare the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false); the description adds real behavioral context the annotations cannot convey: the callback is an outbound POST, it fires only for pages checked in the last 30 days, and the target must be https. It omits whether re-registering replaces an existing webhook and whether the URL is verified before activation.

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?

Three short sentences with no filler, and the core action is front-loaded before the delivery semantics. Nothing is redundant with the schema or annotations.

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 two-parameter registration tool with no output schema, the description covers the action, the delivery trigger, and the auth expectation. The main residual gap is what the call returns (e.g., a webhook identifier or confirmation) and whether registration is idempotent, which matters since no output schema documents the response.

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 50% (url is bare), and the description compensates partially by implying the https scheme requirement for url. However, "Needs a key" reads as mandatory while the schema marks api_key optional and describes it as only raising the daily limit from 25 to 250, which muddies rather than clarifies the parameter.

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?

"Register an https URL" names a specific verb and resource, and the following sentence explains the delivery mechanism (POSTs an alert when a previously checked page is later confirmed hostile). The resource is unique among siblings, so an agent can distinguish it without opening a schema, though no sibling is named as a contrast.

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?

The description implies the use case (you want alerts pushed to an endpoint) and defines the trigger condition via the 30-day window, but it never states when to prefer this over polling tools like my_status or check_url, nor any exclusion such as one-webhook-per-key limits.

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