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

Annotations already establish that this is a read-only, open-world operation. The description adds useful behavioral context beyond the annotations, specifically that it throws GarminError when Garmin returns nothing and that measurements are located under summaryDTO.

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?

The description is short and front-loads the core behavior in the first clause. The remaining details are compact, though the AGENTS.md/spec reference is developer-oriented and slightly less useful for an agent.

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 partially compensates by naming summaryDTO and the underlying type. However, it does not explain the return structure in enough detail and provides no sibling-routing guidance, leaving meaningful gaps for an agent.

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 already documents activityId as a numeric id. The description says "by id" but does not add format, validation, or lookup semantics beyond the schema, so the baseline of 3 is appropriate.

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 phrase "One activity by id" clearly identifies the resource and scope, and an agent can understand it retrieves a single activity. It does not explicitly distinguish itself from close siblings such as get_activity_details, get_last_activity, or get_activities, so it falls short of a 5.

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 description gives no when-to-use guidance, prerequisites, or alternatives. It does not explain when an agent should choose get_activity over get_activity_details, get_last_activity, or list/search tools.

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