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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds useful context by naming the underlying REST endpoint (GET /1/user/-/activities.json), but discloses nothing about auth requirements, aggregation period definition, or freshness of the 'lifetime' totals.

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 tight sentences with no filler: the metric scope is front-loaded and the endpoint provenance is a compact second clause. Nothing could be removed without losing information.

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 no-param, read-only aggregate tool with no output schema, the description adequately covers scope and enumerates the returned metric families. It stops short of describing the response shape or whether 'best-ever' and lifetime totals are returned together.

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?

The tool takes zero parameters, so no parameter documentation is needed; the baseline for a param-free tool is 4. The description confirms the absence of inputs by implying a single fixed aggregate query.

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 specifically that this returns lifetime and best-ever activity statistics (total steps, distance, floors, personal bests), which is clearly distinct from the daily/time-series siblings like fitbit_daily_activity_summary. It lacks an explicit verb and never names a sibling, but the 'lifetime/best-ever' scope makes the resource unambiguous.

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 only implied: the 'lifetime and best-ever' framing signals this is the aggregate view versus the daily or time-series tools, but there is no explicit when-to-use statement, no exclusions, and no named alternative. An agent can infer intent but is given no routing guidance.

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