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

Annotations already declare readOnlyHint=true, and the description adds useful behavior: the lookup is restricted to documented crawlers and returns identity fields, current claims, publication dates, and evidence URLs. This is valuable context beyond the structured fields and matches the closed-world hint (openWorldHint=false), with no contradiction.

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 with no filler: the first front-loads the action and expected output, the second gives targeted usage guidance. Every clause earns its place.

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 single-parameter read-only lookup with strong annotations, the description is complete. It names the input format, the scope, and the output categories; since there is no output schema, enumerating the return fields is necessary and sufficient.

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 description coverage is 100%, and the parameter description already states 'A crawler name, slug, or full user-agent string.' The tool description repeats this without adding new semantic detail, 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 opens with a specific verb ('Look up'), a clear resource ('a documented crawler on Rattlesnakes By Mail'), and the acceptable lookup keys (name, slug, or user-agent string). It also lists the returned fields, making the tool's function unambiguous and distinct from siblings like identify_user_agent.

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 final sentence explicitly states when to use lookup_crawler: when the crawler is already named or the user agent is already known to belong to a documented crawler. This gives clear context and implicitly discourages use for unknown user agents, though it stops short of naming the alternative tool (likely identify_user_agent) explicitly.

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