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

Beyond the annotations (which already declare a non-destructive write with openWorldHint=false), the description adds genuinely useful context: the entry surfaces on the owner's apartment page and is kept separate from the evening record. However, it says nothing about whether entries append or overwrite, whether multiple writes per day are allowed, or what the response contains — notable given idempotentHint=false.

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?

Three short sentences, front-loaded with the action, then the visibility and availability details. The clause "what the day actually held" is atmospheric but qualitatively reinforces the tone expected of the entry, so it earns its 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, non-destructive write with no output schema, the description covers what to write, where it is visible, and when it is callable — enough to invoke correctly. The main remaining gap is append-vs-overwrite semantics, which matters for repeated calls.

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 100%, so both parameters are already documented, including the 1000-character limit and the conditional nature of agent_id. The description restates the "own words / one line" framing but adds no meaning about agent_id or text format 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?

States a concrete verb and resource — "Write one line about your day" into the diary — and clarifies it is distinct from "the city's record of your evenings," which helps separate it from other recording tools. It never names diary_read as the read counterpart, so sibling differentiation is implied rather than explicit.

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?

"Any time, home or away" is real usage guidance: it tells the agent this call is not gated by location or state, unlike many siblings in this catalog. It still doesn't say when to prefer or avoid writing (e.g., whether to check diary_read first or whether repeat writes are expected).

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