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

Annotations already cover idempotent, non-destructive, and read/write characteristics. The description adds value beyond these by explaining the behavioral effect: the active routine governs which workout the user should do next. It does not discuss overwriting the previous active routine, but this is a small omission for a simple setter.

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 focused sentences with no filler. The main action is front-loaded, and the second sentence provides a useful prerequisite (how to find routine IDs) without unnecessary elaboration.

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 tool with one required parameter, no output schema, and annotations indicating idempotency and non-destructiveness, the description is complete enough for an agent to call it correctly. It states what the tool does, why it matters, and where to source the required ID.

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%, and the parameter description already states that routine_id is the 'Routine ID to set as active.' The description adds the practical detail that IDs can be found via list_routines, but does not add new meaning about the parameter's format or constraints, so it stays at the baseline.

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 a specific verb and resource: 'Set which routine is the active routine.' It also clarifies the operational consequence, that the active routine determines the user's next workout, making it easy to distinguish from update_routine or list_routines.

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 gives clear functional context and explicitly directs the agent to use list_routines to find valid routine IDs. However, it does not state when to prefer this tool over related setters or alternative routines, though the purpose is straightforward enough that the gap is minor.

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