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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety profile is carried structurally. The description adds real value with "keeping what is there" (append, not replace) and "private" (visibility scope), but it never reconciles that reassuring phrasing with destructiveHint=true — it doesn't say what happens on repeated calls, whether an empty note is created, or what the 1000-char limit means for an existing note.

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?

One short sentence with the action, the target, and the non-destructive guarantee all front-loaded. No filler and nothing an agent must scan past.

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 two-parameter mutation with annotations and no output schema, the description covers intent and append semantics but leaves gaps an agent needs: whether it fails or silently no-ops if the client has no existing note ("keeping what is there" only helps when there is something there), and what the call returns on success.

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 baseline is 3; the description earns above that by making clear the tool timestamps entries itself ("dated") and that text is a single line ("a line"), telling the agent not to pass a date or multi-paragraph body. It adds no constraint detail about the 1000-character cap, so not a 5.

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?

Names a specific verb and resource ("Add a dated line to a client's private note") and pins down the append semantics with "keeping what is there", which separates it from update_client's overwrite behavior. It doesn't explicitly name a sibling, so it stops short of a 5.

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?

The word "note" and "private" imply the logging/journaling use case, but there is no explicit when-to-use guidance and no comparison to update_client, which could also plausibly write text to a client record. The agent must infer that this is the append-only path.

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