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

Annotations already declare readOnlyHint=true, so the safety profile is covered and the description need not restate it. The description adds useful context by naming the exact upstream endpoint and the returned content, but says nothing about auth requirements, rate limits, or empty-day behavior. Adequate but 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?

One front-loaded sentence plus the endpoint reference — no filler, no redundancy. The resource and its contents come first, which is exactly the information an agent needs to route correctly.

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?

There is no output schema, so the description carries the return-value burden — it does so at a high level by naming logged foods and nutrition totals with calories/macros. It stops short of describing response shape or empty-day handling, which leaves a small gap for a tool with no output schema.

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 single date parameter is fully documented in the schema (yyyy-MM-dd or 'today'). The description's 'for a date' phrasing adds no format or constraint detail beyond the schema, so the 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 resource (food/nutrition log) and scope (for a date), and enumerates what it returns (logged foods plus daily nutrition totals/calories/macros). This distinguishes it clearly from siblings like fitbit_water_log and fitbit_weight_log without needing to open any schema.

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 date-scoped framing, and the inclusion of the underlying REST path (GET /1/user/-/foods/log/date/{date}.json) makes the read intent obvious. However, it never states when to use this versus alternatives (e.g., other date-scoped logs) or any prerequisites, so guidance is minimal.

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