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

Despite having no annotations, the description provides extraordinary behavioral detail, specifying the exact security implementation: HMAC-SHA256 over '<t>.<raw body>', constant-time comparison, and a 300s tolerance. This is critical technical behavior an agent needs to know.

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?

While dense, the description is highly efficient. Every sentence contributes technical, actionable information (algorithm, input format, error handling) rather than filler. It sacrifices absolute brevity for necessary technical specification.

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?

Even without an output schema, the description fully discloses the return structure: 'valid=true/false with the reason and the parsed event.' This makes the tool definition complete for an agent to decide if/how to invoke it.

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?

The description adds high value beyond the 80% schema coverage by detailing the required format of input data, such as 'exact raw request body (no re-serialisation),' the structure of the signature header ('t=...,v1=...'), and the operational context for the secret and timestamp controls.

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 purpose is specific: to verify a webhook delivery locally without making an API call. It identifies the specific security mechanism (CoinVello-Signature) and distinguishes its function from other transactional tools like create_webhook.

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?

It provides explicit usage context by stating the verification happens 'locally (no API call)' and gives a specific scenario for a parameter: 'Set ignore_timestamp=true when checking an old captured delivery.' This defines its boundary perfectly.

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