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

Beyond the comprehensive annotations (readOnlyHint, idempotentHint, openWorldHint, destructiveHint), the description adds important behavioral details: does not execute JavaScript, restricts to public URLs, rejects SSRF-sensitive destinations, and clarifies cache behavior with 'fresh'. No contradictions.

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 concise sentences, no wasted words. First sentence states core purpose, second clarifies scope, third gives parameter guidance. Information is front-loaded and easy to parse.

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?

Given the tool's low complexity (2 params, no nested objects), rich annotations, and existence of output schema, the description completely covers all usage aspects: input constraints, cache behavior, and limitations. No gaps remain.

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% with both parameters documented. The description adds value by explaining the 'fresh' parameter's cost implications ('cheaper for the origin') and reiterating URL requirements, which improves agent understanding beyond 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?

The description clearly states 'Resolve requested, final and declared canonical URLs with evidence', specifying the exact verb and resource. The title 'Url Canonical' and the unique function among siblings (canonicalization vs other URL features) make purpose unambiguous.

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 description provides explicit usage instructions: 'Use only for public HTTP(S) resources', notes limitations (no JavaScript, no access control bypass), and explains when to set 'fresh' parameter. It lacks explicit references to sibling alternatives but sufficiently guides correct invocation.

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