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

Annotations already indicate destructive and non-idempotent behavior. The description adds valuable context: it rejects embedded credentials, never validates destination content, and states the price and wallet authorization requirement. This goes beyond the annotations and helps the agent understand side effects (payment) and limitations.

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 concise (four sentences) and front-loaded with the primary purpose. Each sentence adds distinct information: main function, duplication behavior, security/validation disclaimer, and pricing/authorization. No wasted words.

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?

With five parameters, a nested input schema, and no output schema, the description omits explanations for several parameters (payment, idempotency, signatures). While the UTM and URL aspects are covered, the tool's full contract (how to authorize payment, what the result format is) remains underspecified, making it incomplete for an agent to invoke confidently.

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 0%, so the description must compensate. It explains the role of UTM fields (encoding, duplication handling) and the preservation of unrelated parameters, which aids the 'url' and 'utm_*' inputs. However, it does not clarify the purpose of result_expires, idempotency_key, result_signature, or payment_signature, leaving these parameters ambiguous for an agent.

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 clearly states a specific verb ('Build'), a precise resource ('HTTP(S) campaign URL'), and the core function (adding UTM fields) while distinguishing it from sibling content-generation tools. It also specifies that unrelated query parameters and fragments are preserved, which sets clear boundaries for the tool's behavior.

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 provides clear context for when to use this tool: whenever a campaign URL with UTM tracking is needed. It does not explicitly name alternatives or exclusions, but the unique purpose is evident from the description and sibling list, making it unlikely an agent would confuse it with other tools.

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