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

Annotations declare readOnlyHint=true, so the safety profile is covered. The description adds real behavioral value beyond that: the 1095-day maximum range, which is a genuine invocation constraint, plus the underlying REST endpoint for traceability. It omits pagination/return-format detail, but the cap and read-only nature are the key facts.

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 compact sentences, front-loaded with the purpose, then the constraint, then the endpoint reference. No filler, though the raw REST path is slightly redundant for an agent that will not call it directly.

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 read-only, three-parameter tool with full schema coverage and no output schema, the description supplies the purpose, an example, and the range cap. Return format is unspecified, but a time-series tool does not strictly require it for correct invocation.

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 description coverage is 100%, and the parameters carry patterns, enums and semantics already. The description's example ('daily steps for a week') lightly reinforces how resource/dates combine, but adds no syntax beyond what the schema already documents. 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 specific verb+resource (activity metric time series over a date range) with a concrete example ('daily steps for a week'), which tells an agent exactly what it returns. It distinguishes itself implicitly from fitbit_daily_activity_summary by emphasizing a date-range series, though it doesn't name that sibling 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?

Provides context (date-range series, example of a week) and a hard constraint (max 1095 days), but never says when to prefer this over fitbit_daily_activity_summary or fitbit_lifetime_stats. Usage is implied rather than directed.

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