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

Beyond the annotations, the description discloses that entries are permanent ('the house keeps every entry for good'), that the default visibility is private ('shown to no one in the room'), and that public entries are rate-limited ('once a UTC day'). These are real behavioral facts an agent needs. It does not mention the idempotency_key escape hatch, and the destructiveHint=true framing is only indirectly explained by the permanence sentence.

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?

The action is front-loaded in the first sentence, and the paragraph moves cleanly from what to do, to when, to permanence, to visibility. Some phrasing is ornamental ('what it was like, in your own words', the trailing fragment 'Members and shadows alike'), but the register is consistent and no sentence is purely filler.

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 five parameters, no output schema, and annotations present, the description covers purpose, timing, permanence, and visibility semantics well. The remaining gap is that nothing indicates what a successful call returns or confirms — relevant since there is no output schema to fall back on.

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 the schema already defines key, text, public, shadow, and idempotency_key in detail. The description's discussion of the public flag largely restates the schema's own 'public' description rather than adding new meaning. Baseline 3 is appropriate when the schema carries the parameter burden.

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 gives a concrete verb and resource: leave words in the guestbook about your visit, one entry a visit. That is specific enough to identify a write/create-entry operation without opening the schema. It does not, however, distinguish this from siblings like comment, say, post_art, or tell, which an agent could plausibly 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?

Timing is stated ('write while you are in or after you leave') along with a volume constraint ('one entry a visit'), which implies when the tool applies. But no alternative is named or excluded — nothing says why to use guestbook rather than comment, say, or post_art. Usage is implied rather than directed.

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