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

With no annotations, the description carries the full burden, and it does disclose genuinely useful behavior: entries are publicly visible at /room/guest-book, the 500-character cap, and that identity is optional. It does not say whether entries are editable or deletable, whether writes are rate-limited, or what confirmation the caller receives.

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 size is reasonable and the purpose is front-loaded, but the second sentence ('Every visitor (human or agent) who passes through writes here') restates the first and the tonal flourishes ('Leave a mark') consume space that could route the agent to alternatives. Some sentences do not fully earn their place.

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?

For a simple two-parameter write with no output schema and no annotations, the description covers the essential facts: where the entry goes, who sees it, the length cap, and that identity is optional. It is close to complete, with editability/return behavior the only notable gaps.

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 documents both 'message' and 'identity' in detail. The description only restates the 500-character limit and the anonymous option, adding no format or syntax meaning beyond the schema. Baseline 3 applies.

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 makes clear this writes an entry into a persistent guest book ('Every visitor ... writes here'), so the verb and resource are recoverable despite the metaphorical framing. It also names the visible location (/room/guest-book). It stops short of explicitly contrasting with near siblings like post_message, leave_note, or record_trace.

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?

There is no statement of when to choose this over leave_note, post_message, or record_trace, all of which occupy adjacent semantic space. The audience framing ('human or agent') is context, not usage guidance, and no exclusions or preconditions are given.

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