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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds valuable behavioral context beyond that: the exact return object shape, the fact that invalid input is rejected before billing, and the per-successful-call pricing model. It does not cover rate limits or secret-handling, but the schema notes the secret is not stored, so the remaining gap is minor.

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?

The description is front-loaded with the core purpose and provider list, then adds return shape and billing constraints in compact form. Every sentence carries useful information, though the billing sentence could theoretically be trimmed if cost were documented elsewhere. Overall it is well sized and efficient.

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, but the description explicitly states the return shape ({ provider, valid, timestamp?, age_s?, within_tolerance? }), which closes the main gap. It also documents billing and validation behavior. The only missing element is explicit secret-handling guidance, which the input schema already covers, so the description is effectively complete for calling the tool correctly.

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 description coverage is 100%, so all six parameters are already well documented in the schema. The description only reinforces provider names and timestamp tolerance at a high level, without adding syntax or format details beyond what the schema provides. Baseline 3 is appropriate when the schema does the heavy lifting.

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 names a specific verb (verifies) and resource (webhook signatures), enumerates the supported providers, and explains the verification approach (exactly as the provider computes them, with timestamp tolerance). It is immediately distinguishable from every sibling tool, none of which deal with webhook signature verification.

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 makes clear this is for verifying provider webhook signatures and lists the exact schemes supported, which tells an agent when the tool applies. It does not explicitly name when not to use it or point to an alternative, but no sibling tool overlaps this function, so the practical guidance is sufficient.

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