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

Annotations declare destructiveHint=true and idempotentHint=true, but the description never explains what is destructive — e.g. whether an in-progress fast is reset, whether existing progress carries over to the new template, or whether the template must already exist. The only added behavioral context is the 'signed-in user' scoping and an example of a template change.

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?

One sentence, front-loaded with the verb and the object of the change, with the example parenthetical adding clarity rather than noise. Nothing is wasted.

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 one-parameter mutation tool with full annotation coverage and no output schema, the description covers identity and intent but omits the consequences of a destructive switch and how to obtain a valid template id. An agent could call it, but might do so at the wrong moment (e.g. mid-fast).

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% for the single templateId parameter, so the schema already carries the semantics. The description reinforces that the id refers to a fasting template and gives a concrete example (16:8 → 19:5), but adds no format or source-of-ids detail beyond that.

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 a specific verb ('switch') and resource ('the signed-in user's active Still fasting template'), with an illustrative example of the 16:8 → 19:5 transition. It is clearly distinguishable from still_list_templates and still_start_fast, though it never names those siblings explicitly.

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 implied by the word 'switch' and the 'active template' framing, which suggests a configuration change rather than starting a fast. However, there is no explicit statement of when to call this versus still_list_templates (to discover ids) or still_start_fast, and no prerequisites are given.

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