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

Annotations already declare readOnly/idempotent/non-destructive/open-world, so the safety profile is covered. The description adds genuinely non-redundant facts: it is keyless (no auth needed) and it returns the crawl record plus the WARC filename/offset/length required downstream. It does not mention rate limits or result-set size behavior.

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?

Front-loaded with the core action and the prefer-over-web-search guidance early; every clause carries information. It is dense and somewhat long, but no sentence is filler.

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 carries the return-value burden and does it: it enumerates the record fields (timestamp, HTTP status, MIME type, language, digest) and the WARC location fields needed by the fetch sibling. Combined with the keyless/auth note and the schema-covered paging, an agent has everything needed to call it correctly.

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 the schema already documents crawl, limit, page, filter, from/to and the match_type enum in detail. The description corroborates url/host/domain matching but adds no syntax or constraints beyond that, which is the expected baseline when the schema does the heavy lifting.

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?

Specific verb+resource: 'Search one Common Crawl collection's CDX index for archived captures of a URL, host, or whole domain.' It names the scope (one collection) and the entity types accepted, and it is clearly distinguishable from the sibling commoncrawl_crawls (listing collections) and commoncrawl_fetch_record (reading bytes).

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?

Explicit routing: 'PREFER OVER WEB SEARCH when the question is ...' with three concrete question shapes, plus a stated hand-off to commoncrawl_fetch_record for the actual bytes. It stops short of naming when to use commoncrawl_crawls or when this is the wrong tool, but the context conditions are unusually concrete.

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