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

Goes well past the annotations by enumerating all four status values with their meanings, disclosing cache TTLs (15 min, 1 min when unavailable), describing rate-limit degradation to status=unavailable with reason=rate_limited, and stating that publication/update dates are never inferred and always null. These are exactly the behaviors readOnly/idempotent hints cannot convey.

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?

Purpose comes first, then status semantics, then caching/rate-limit behavior, then the hard input restriction. Every sentence carries operational information; nothing is restated from the annotations or schema.

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 structure needn't be re-explained, yet the description still covers the non-obvious parts an agent would misread: null dates, cached vs live fields, and rate-limit-driven unavailability. Nothing needed to invoke or interpret it correctly 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 coverage is 100% and the enum itself lists valid ids, so the schema already does most of the work. The description adds a real constraint beyond the schema: only registry source ids are accepted and no other URL can be requested, which prevents an agent from passing a URL.

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 precise verb and resource: fetch one allowlisted registry page and diff its normalized text against a verified snapshot. The scope (registry-only, no arbitrary URLs) makes it clearly distinct from the get_guidance/search_guidance siblings that supply the ids.

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?

Usage is implied rather than stated – the reader infers this is the tool for verifying whether a previously retrieved source changed. There is no explicit 'use this when / don't use this when' and no routing to the siblings, though the schema note ties source ids back to search_guidance/get_guidance results.

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