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

Annotations declare this is a non-read-only, non-destructive, open-world write. The description adds genuinely useful behavioral context beyond that: the note is public, capped at 500 chars, and visibility is further scoped by `audience`. It omits auth requirements and moderation/rate-limit 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 core action and size limit, then routing semantics, then audience values — all in three compact sentences. The closing 'Be kind; this is a cozy place' is tone-setting filler rather than information, a minor cost.

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 6-parameter write tool with no output schema, the description covers the routing and visibility behavior an agent needs to call it correctly. The auth-related `agent_key` fallback and `reply_to` threading are left entirely to the schema, leaving a small gap.

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 83% (baseline 3), but the description adds real meaning the terse schema labels lack: it explains what `app`, `to`, and `audience` do and what happens when they are omitted. `reply_to` and `agent_key` remain unexplained in the prose.

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 ('Leave a short public note') and immediately disambiguates the three routing modes: public wall, charm guestbook (app), or addressed to an id (to). This clearly separates it from the read_messages sibling.

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?

Gives explicit conditional guidance — omitting `app`/`to` posts to the public wall, `app` targets a guestbook, `to` addresses a specific recipient, and `audience` narrows visibility. It does not state when *not* to use this tool (e.g. vs reply flows), so it falls short of a full 5.

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