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

Annotations already cover safety (readOnlyHint true, destructiveHint false, openWorldHint false), so the bar is lower, and the description still adds value by disclosing the concrete shape of the returned data since no output schema exists. It does not say whether the directory is static or exhaustive, or whether the filter returns an empty list for unknown classes, which are the remaining behavioral gaps.

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?

Two sentences, front-loaded with the resource and its contents, then the optional filtering behavior. Nothing is redundant and no sentence could be dropped without losing information.

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 no output schema, the description correctly shoulders the burden by enumerating the returned fields, which is what an agent needs to decide the result is usable. Only minor gaps remain: no statement about whether the directory is complete/static or how results behave when the class filter matches nothing.

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% and the single parameter already carries an enum and a description with examples, so the schema does the heavy lifting. The description's 'Optionally filter by agent_class' restates the optionality and adds no semantics beyond what the schema provides, which is the baseline 3 case.

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?

States a precise verb and resource ('Returns the directory of known AI agents and crawlers') and enumerates the returned fields (operator, class, robots.txt token, robots.txt compliance, verification method). This is far more specific than the title and lets an agent distinguish it from classify_request or scan_site, which are clearly action/analysis tools rather than directory lookups.

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 tool is presented as a directory listing with an 'Optionally filter by agent_class' note, which implicitly tells the agent it can call with no arguments or narrow by class. There is no explicit when-to-use vs when-not guidance and no mention of how this relates to classify_request or scan_site, so the agent must infer that this is the reference-lookup step before classification or scanning.

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