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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds the meaningful behavioral detail that the baseline is the previous scan by default and the newest scan on or before a date when compare_with_date is supplied. It does not say what happens when no prior scan exists, but the comparison semantics themselves are well disclosed.

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, both earning their place: the first defines the operation and its outputs, the second gives usage triggers. Front-loaded with the core comparison before the usage hint.

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 compensates by enumerating the returned diff categories, and it explains both the default and date-anchored comparison modes. For a two-parameter read-only tool, 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 both parameters already carry their own documentation (domain must be a monitored domain; compare_with_date selects the newest scan on or before that date). The description restates the date-baseline behavior without adding syntax, format, or edge-case detail beyond the schema, so 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?

Specific verb (compares) plus specific resource (latest scan vs previous/date-anchored scan of a monitored domain), and it enumerates the diff categories produced: new issues, resolved issues, score change, banner and reject option changes. That enumeration distinguishes it clearly from siblings like get_findings or scan_history, which return state rather than a delta.

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?

"Use it to confirm a fix worked or to see what a site update broke" gives concrete triggering scenarios, so an agent knows when a diff is the right tool. It stops short of naming alternatives or exclusions (e.g. use scan_history for older baselines), so it is clear context rather than full routing guidance.

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