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

The readOnlyHint annotation already establishes this as a safe read, so the bar is lower. The description adds the underlying REST route (GET /1/user/-/activities/goals/{period}.json), which confirms read semantics, but says nothing about auth, rate limits, or whether goals can be absent for a period.

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 short sentences with the substantive content front-loaded; nothing is padded. The raw REST path is arguably noise for an agent caller, which keeps this just short of a 5.

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 one-parameter read tool with no output schema, the description usefully enumerates the returned goal fields and the two periods, so an agent knows what to expect. Missing only edge-case behavior (e.g., absent goals), which is minor here.

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 enum parameter is fully documented, so the baseline is 3. The description restates the same 'daily or weekly' options and adds no syntax or format detail beyond the schema.

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 the specific resource (the user's activity goals) and enumerates the fields returned (steps/distance/calories/active-minutes) plus the two valid periods. It clearly distinguishes this from siblings like fitbit_daily_activity_summary, which reports actuals rather than goals, though it never names an alternative 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?

There is no statement of when to use this tool versus alternatives such as fitbit_daily_activity_summary or fitbit_lifetime_stats. The only usage signal is the required period parameter, which is already in the schema, so the agent gets no routing guidance.

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