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

Annotations already declare read-only, idempotent, open-world, non-destructive. The description adds attributes annotations cannot express: it consumes one backlinks call from the monthly quota, 'removed' means only not-observed in the newer snapshot (not proven live-web deletion), and comparison_available:false is a legitimate success state. These are exactly the behavioral caveats an agent needs.

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?

Four tight sentences, each carrying distinct information (purpose, defaults, cost, interpretation caveat, valid edge-case response). The core action is front-loaded and nothing is redundant.

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?

An output schema exists, so return-value documentation is not required, yet the description still covers the one return state an agent could misread as failure (comparison_available:false). With quota cost, default behavior, and result interpretation all addressed, nothing material is missing.

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 baseline is 3, but the description adds the non-obvious default behavior: both release parameters are optional and the API selects the newest queryable pair when omitted. That is semantic value beyond the schema's terse 'Newer/Older Common Crawl release id' strings.

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 ('Compare referring-domain observations between two Common Crawl releases'), which clearly separates it from the sibling 'backlinks' (single snapshot) and 'releases' (release listing). An agent can tell what it does 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?

Explains the default path when from_release/to_release are omitted (API picks the newest queryable pair) and notes the quota cost, which frames when the call is worthwhile. It does not explicitly route an agent to alternatives such as 'backlinks' for single-release data, so routing guidance is implied rather than stated.

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