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

readOnlyHint=false already marks this as a write, and the description usefully adds the preview-until-confirm protocol. The critical behavioral unknown for an 'upsert' with all-optional metric fields is not disclosed: whether omitted metrics are cleared, left untouched, or whether the whole day's record is replaced. That merge-vs-replace semantics gap matters for a mutation tool.

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?

Two compact sentences, front-loaded with what is written and followed by the confirm protocol. Nothing is redundant against the title or schema.

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 nested-object write tool with no output schema, the description covers the target resource, the field set, and the confirm gate. The remaining gap is overwrite semantics and what the preview returns, which keeps it from being complete.

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 only 50%, but the description compensates by mapping friendly names to the raw field names ('water glasses' -> glasses, 'resting HR' -> restingHeartRate) and stating the one-day scope of date. Units and whether partial field sets are permitted remain unspecified, so it stops short of full compensation.

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 (set/upsert) and resource (a client's daily metrics for one day) and enumerates exactly which five metrics are covered. An agent can distinguish it from get_client_daily_metrics by the write verb, though it never names the read sibling or any other writer explicitly.

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 confirm-gating note tells the agent how to invoke it safely (preview first), which is real usage guidance. However, it never says when to choose this over alternatives such as log_client_habit or the check-in tools, nor what prerequisite data (a valid clientId from list_clients) is required — that is left to the schema.

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