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

Annotations declare idempotentHint=true, readOnlyHint=false, destructiveHint=false. The description adds the behavior that passing null clears the keyword, which is important context. It also states the character limit (2-10) which is a constraint. Since annotations already indicate idempotent and non-destructive, the description doesn't need to repeat those. It adds the clearing behavior and the routing effect, which exceeds what annotations provide.

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 two sentences, with the core action and constraint front-loaded. The null-clearing behavior is mentioned second, which is useful. No wasted words; every sentence adds value.

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?

Given the tool has only one parameter with full schema coverage, an output schema exists (though not shown in details), and annotations cover idempotency and destructiveness, the description is fairly complete. It could mention what the response will be or any side effects, but for such a simple configuration tool, it's adequate. The output schema likely covers return values. No major gaps.

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% - the schema describes the keyword as a string of 2-10 alphanumeric characters or null. The description adds the functional meaning: the keyword routes inbound SMS. But it doesn't add syntax or format beyond the schema's pattern. Since the schema is fully descriptive, baseline 3 is appropriate.

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 ('Set') and resource ('inbound keyword'), and defines the exact function: routing inbound SMS that start with the keyword to this account. It also distinguishes itself by mentioning the null-clearing behavior. While it doesn't explicitly name a sibling, the purpose is unambiguous and not a tautology.

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 explains when to use the tool: to set a keyword so inbound SMS starting with it are routed to the account. It doesn't explicitly state when not to use alternatives, but the context is clear: it's for inbound routing configuration, distinct from send_sms, list_messages, etc. It would be better to mention that null clears the keyword, which it does. No explicit exclusion, but the purpose is clear enough for an agent to differentiate.

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