lookup_rcs

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It only says 'check RCS capabilities', which implies a read-only operation, but it does not disclose what capabilities are checked, error conditions, rate limits, or the response format. This is insufficient for an agent to understand the tool's behavior.

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 a single, short sentence that is front-loaded and efficient. However, it may be too concise, omitting important details that would improve usability. It earns its place but could be expanded slightly.

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 simplicity of the tool (single required parameter, no output schema), the description is minimally adequate. However, it lacks context about what RCS capabilities entail, expected return values, and error handling. More detail would improve completeness.

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 input schema has 100% coverage with the parameter 'number' described as 'Phone number to check RCS capabilities'. The description repeats this information without adding new meaning or constraints beyond what the schema already provides. Since coverage is high, baseline is 3, but no additional value is added.

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 'Check RCS capabilities for a phone number' clearly states the action (check) and the resource (RCS capabilities for a specific number). It distinguishes itself from sibling lookup tools like lookup_cnam, lookup_format, lookup_hlr, and lookup_mnp, which serve different purposes.

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 does not provide any guidance on when to use this tool versus its siblings or alternatives. There is no mention of context, prerequisites, or conditions that would help an agent decide to invoke lookup_rcs instead of other lookup tools.

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