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

readOnlyHint=true already tells the agent this is a safe read, so the bar is lower. The description adds the Fitbit REST endpoint and scope (single date vs range), but says nothing about rate limits, pagination, or error behavior for the API path.

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 tightly packed sentences with zero filler; the payload description is front-loaded and the REST endpoint is relegated to a supporting clause.

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 usefully enumerates what a sleep log contains, which compensates for the missing return schema. Only rate-limit and pagination behavior remain unstated, which is minor for a read-only log tool.

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 schema documents both parameters including the max 100-day range constraint. The description's 'date (or date range)' maps to the two params but adds no format or constraint detail beyond the schema, so 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 and resource ('Sleep logs for a date') and enumerates the returned fields (stages/levels, duration, efficiency, start/end). The sleep resource is naturally distinct from the activity, heart-rate, and weight siblings, though no sibling is named 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 parenthetical '(or date range)' implies the two calling modes, but there is no explicit when-to-use guidance, no prerequisites, and no mention of alternatives such as other time-series sleep tools. Usage must be inferred.

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