list_activities

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description goes well beyond that with non-obvious behavior. It discloses the ordering quirk ('newest first, but oldest first when `after` is set') and the pagination signal (`more_available` is true when the page came back full), both of which an agent would otherwise misread. Those are exactly the kind of behavioral traits annotations cannot express.

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?

Four short sentences, zero filler. Scope and field list come first, then the two behavioral quirks, then the alternative-tool routing at the end. Every sentence carries information an agent needs.

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 read-only paged listing with an output schema present, the description need not explain return structure, yet it still summarizes the field set helpfully. Combined with ordering, pagination, and alternative-tool guidance, nothing an agent needs to call this correctly is missing.

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 coverage is 100%, so both the pagination params and the ISO date bounds are already documented, giving a baseline of 3. The description adds real meaning on top by tying `after` to a change in result ordering and by explaining how the page-full signal interacts with paging. It doesn't add format details for `before`/`per_page` beyond the schema, so it lands at 4.

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 opens with a specific verb and resource ('The connected athlete's activities as compact summaries') and then enumerates the actual fields returned (sport, distance, moving time, heart rate, power, etc.). It clearly separates itself from get_activity, which returns full detail for a single activity, so an agent can pick the right tool without opening either 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?

It explicitly names the sibling alternative and the condition that selects it: 'Use get_activity for one activity's full detail.' It also tells the agent how to continue paginating ('more_available is true when the page came back full, so ask for the next page'). It stops short of full when/when-not coverage (e.g., no guidance on list_starred_segments or segment efforts), so a 4 rather than a 5.

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