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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety/idempotency profile is covered. The description adds little behavioral context beyond input normalization; it does not discuss pagination behavior or any other trait not already implied by the annotations and output schema.

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?

Three compact, front-loaded sentences: purpose, invocation constraint, and return contents. Zero waste overall, though the closing 'Returns…' sentence partially duplicates what the output schema already documents.

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 full schema coverage, annotations, and an output schema, the description supplies enough to invoke the tool correctly (mode selection, normalization, return shape). Pagination via offset/next_offset is left entirely to the schema, a minor gap for a paginated lookup.

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%, so all five parameters are documented in the schema itself, including the ':'/'://' normalization and the scheme-or-keyword mutual exclusion. The description largely restates these facts and adds no meaning about limit, offset, or status beyond what the schema provides, so the baseline 3 applies.

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 specific verb and resource (look up a registered URI scheme), and the resource is distinct from every sibling (http field, http status, language tag, media type, pen, port, registry records). An agent can identify the right tool from the description alone without opening the schema.

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?

Clearly specifies the two operating modes and the constraint 'Pass exactly one of `scheme` or `keyword`', with examples for each. It does not, however, contrast this tool with alternatives such as iana_search_registries, so no explicit when-not guidance is offered.

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