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

Annotations already declare readOnly, non-destructive and closed-world, so the safety profile is covered. The description adds real behavioral detail beyond that: the default page size of 10, the 1-50 cap, and the rule that end_date falls back to today when start_date is supplied — all directly useful for shaping a call.

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?

Front-loaded with the return shape, then a compact Args block with one line per parameter; nothing is redundant. The swim-detail sentence is slightly granular but still earns its place by signalling the field-level variation in results.

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?

An output schema exists, so return values needn't be enumerated, yet the description still flags the notable swim-specific fields (pool length, SWOLF, stroke rate). Combined with complete parameter semantics and annotation-covered safety, an agent has everything needed to invoke this correctly.

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 0%, so the description carries the full burden and does: it gives limit's bounds and default, start_date's YYYY-MM-DD format and role as range start, and end_date's conditional default. That is meaning the bare schema (types and nulls only) does not provide.

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 concrete resource and scope: recent runs/rides/swims with distance, duration, pace and HR zones, which clearly separates it from the singular get_activity_details. It stops short of explicitly naming that sibling or stating the listing boundary, so differentiation is by implication rather than statement.

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 through the date-range parameters; nothing says when to call this versus get_activity_details or get_daily_summary, nor what happens with no arguments. The caller can infer the list-vs-detail split, but the description doesn't guide it.

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