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

With no annotations, the description carries the behavioral burden. It does state the core behavior: checking presence across 16 public sites. However, it does not disclose rate limits, exact-match behavior, authentication needs, or what happens when q is empty. These gaps are notable but the main behavior is at least visible.

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 front-loaded sentence: 'Username Hunter: Presence across 16 public sites.' It is efficient and scannable, with no filler. It is concise without being bloated, though it sacrifices some useful detail for brevity.

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?

For a one-parameter tool with an output schema, the description provides enough high-level context to begin using it. However, it leaves important aspects undocumented: the meaning of q, behavior on empty input, and how the 'presence' result is represented. It is viable but not fully complete.

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 schema only defines q as a string with a default of empty string and no description. The tool description never explicitly states that q is the username to search. The title makes this partially inferable, but the description does not compensate for the 0% schema description coverage.

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 identifies the resource ('username') and the intended outcome ('presence across 16 public sites'). It is more specific than a generic 'lookup username' and conveys a concrete aggregation function, though the phrasing is more label-like than a full verb phrase.

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 implies a use case—checking where a username exists across public sites—but gives no explicit when-to-use guidance, no exclusions, and no contrast with sibling tools like social, github, or other username-related lookups. An agent would have to infer when this is the right choice.

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