lookup_profile

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

No annotations are provided, so the description must fully convey behavioral traits. It only mentions a permission requirement and implies a read operation (look up), but does not disclose rate limits, error handling (e.g., if user not found), or other side effects. This is insufficient for a tool with zero annotation support.

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 consists of two concise sentences, each adding value: the first states the purpose, the second adds a usage prerequisite. No extraneous information, well front-loaded.

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's simplicity (lookup by username, optional fields), the description covers the essential purpose and permission requirement. However, the absence of an output schema means the agent lacks information about return values, but for a straightforward lookup tool, this is a minor gap.

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 already describes both parameters (username and fields) with 100% coverage. The description adds no additional meaning or context beyond what the schema provides, so the baseline score of 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 the tool's action ('Look up') and resource ('Threads user profile by username'), making its purpose unambiguous. It uses a specific verb and resource, and while there is a sibling 'get_profile', the mention of 'by username' differentiates it.

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 includes a prerequisite ('Requires threads_profile_discovery permission'), which provides context for when the tool is usable. However, it does not specify when to use this tool over alternatives, nor does it offer exclusions or guidance on when not to use it.

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