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

Annotations already declare readOnly/idempotent/non-destructive, and the description reinforces this with 'it does not write anything' and 'Returns the file and whether the site already has one'. It further discloses filtering rules (noindex, non-200, canonicals to another address excluded) and shallowest-first ordering, which go beyond the annotations.

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 dense sentences that front-load the artifact and format, then sourcing/filtering, then return behavior. No filler, though the parenthetical format explanation and sourcing clauses are packed tightly.

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 still states the return payload (the file plus whether one already exists) and covers sourcing, exclusion rules, ordering, and the no-write guarantee. 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?

At 67% schema coverage the description compensates: it clarifies that `urls` sets priority order and is capped at 100, and that `name`/`summary` override the derived values. It also explains `language` behavior (one language, unprefixed default) and page limits, adding real meaning over the raw 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 and artifact ('Build an llms.txt for a site') and immediately names the format standard (llmstxt.org) and its contents. No sibling tool produces this artifact, so it is unambiguous against the catalog.

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?

Explains where pages are sourced (sitemap or home page links) and recommends passing `urls` to prioritize, citing gsc_performance_overview as a concrete source. It stops short of stating when NOT to use it or naming an alternative tool, but the operational context is clear.

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