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

Annotations already cover the safety profile (readOnlyHint, openWorldHint), and the description adds genuinely new behavior: the fetch is a single non-JS raw HTML read, so JS-rendered content will be invisible. It also discloses the auth/cost model ("needs an API key but no balance"), which is real operational context not present in the structured fields. It stops short of stating rate limits or failure behavior.

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?

Front-loaded with the verb and resource, then the return payload, then the sibling pointer and the free-tier note — each clause carries distinct information. No filler or 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 no output schema, the description compensates by enumerating the returned fields, and it covers the JS limitation and access requirements. Minor gaps remain: no indication of how errors, redirects, or large pages are reported, and the "free/no balance" phrasing is compressed enough to be slightly ambiguous.

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%, including the enum values and the cloaking rationale for fetch_as, so the description is not required to carry parameter meaning. "As a browser or as Googlebot" loosely restates the enum rather than adding syntax, defaults, or edge cases. Baseline 3 applies when the schema already does this work.

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 ("Fetches one URL") and then enumerates exactly what comes back: status, final URL, title, meta description, canonical, meta robots, X-Robots-Tag, hreflang and H1s. The parenthetical "For a full audit use page_audit" separates it from the closest sibling, so an agent can pick between the two without opening either 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?

Names an explicit alternative and the condition that selects it (full audit → page_audit), and implies the fetch_as=googlebot path is for cloaking checks. It does not spell out exclusions against other near neighbours such as redirect_chain (which also surfaces status/final URL) or check_robots, leaving some routing inference to the agent.

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