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

readOnlyHint=true already establishes the safe-read profile, so the bar is lower. The description usefully adds the return shape and the underlying REST call, but says nothing about auth requirements, rate limits, or how large ranges are handled beyond what the schema states. Adequate, not rich.

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. The functional scope leads, the returned fields follow, and the endpoint reference is tucked at the end — no filler and nothing front-loaded incorrectly.

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 no output schema, the description compensates by naming the returned fields, and it covers both single-date and range invocation. It is complete for a two-parameter read tool, though it omits any note on response structure or paging for long ranges.

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%, so date/endDate formats and the max 100-day range are already documented in the schema. The description echoes 'date (or date range)' without adding syntax or edge-case meaning, which matches the baseline-3 expectation when the schema does the heavy lifting.

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 ('Sleep logs for a date or date range') and enumerates the payload (stages/levels, duration, efficiency, start/end times), which cleanly separates it from siblings like fitbit_hrv, fitbit_breathing_rate, or fitbit_activity_time_series. The REST endpoint mapping pins down exactly which data source it hits.

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?

Usage is implied by the resource name and the date/date-range scope, but there is no explicit when-to-use guidance and no alternatives named. An agent can infer the intent, but nothing steers it away from a sibling tool if the request is ambiguous (e.g., a general 'health today' query).

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