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

Annotations already establish the safe read-only profile (readOnlyHint=true, destructiveHint=false), so the description only needs to add nuance. It does so usefully by disclosing that streak and best are computed within the supplied range, which changes how the agent picks a range value. It stops short of return-format or pagination notes, but those are covered by the output schema.

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 tight sentences, front-loaded with the returned metrics and immediately followed by the routing rule and the range caveat. Every clause carries information; nothing is filler.

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?

With an output schema documenting returns and annotations covering the safety profile, the description supplies everything else an agent needs: what is summarized, which sibling to prefer, and the tricky range/streak interaction. Nothing material is missing.

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 adds meaning beyond the schema by explaining the interaction between the range value and the streak metric ('counted within the range, so pass 90d or all'), which is genuine guidance the schema's enum description does not provide.

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 names a specific verb (summarize) and enumerates the exact outputs (totals, today, daily average, streak, best day, goal progress) scoped to a topic over a range. It is instantly distinguishable from siblings like query_entries, which it explicitly contrasts against.

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?

It states a direct preference rule ('Prefer this over query_entries for "how was my week"'), naming the alternative and the triggering condition. It also gives an actionable hint ('pass 90d or all to find a long streak'), covering when-to-use at a practical level.

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