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

Annotations already cover readOnly/idempotent/openWorld, so the description's job is to add context, and it does: private addresses are refused (SSRF guard), responses are size-capped, and probing reports a sample of HTTP statuses rather than exhaustive checks. That constraint and safety detail is real value beyond the structured hints; only rate-limit/timeout behavior is left unstated.

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 short sentences, front-loaded with the primary validate job, then the generate mode, then the two operational constraints. Zero filler and no restatement of the tool name.

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 an output schema present, return values need not be described, and annotations carry the safety profile; the description covers both modes plus the SSRF and size-cap constraints an agent needs to invoke it correctly. Minor gaps remain around probe=false behavior and precedence rules, though precedence is partly covered by the schema.

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 four parameters are already documented, making 3 the baseline. The description reinforces semantics ('a sample of HTTP statuses' for probe, urlset generation for urls) but adds no syntax, defaults, or limits beyond what the schema provides (e.g. the 5000-item maxItems is only in the schema).

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+resource pair ('Validate sitemap XML or a public sitemap URL') and explicitly covers the second mode ('Or generate a urlset from a list of URLs'). This distinguishes the two behaviors internally, though it never names a sibling tool (e.g. check_robots_txt or generate_llms_txt) that an agent might confuse it with.

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 'Validate ... Or generate ...' construction plus the schema note that urls overrides url/xml gives clear selection context for each mode. It does not state when NOT to use the tool or point to an alternative, so it stops short of explicit routing guidance.

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