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

Annotations already establish read-only, non-destructive, closed-world behavior, so the bar is lower. The description adds real context beyond them: the returned fields and the `zone` semantics, including the instruction to flag and confirm when the zone reports UTC and the athlete may already be on a different calendar day.

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 core fact, then the call-to-action, then the caveat — a sensible order with no filler. The em-dash-heavy sentences are dense and slightly over-packed, but every clause carries distinct information.

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 carries the return-value burden and does so by naming the ISO date, weekday, ISO week, and zone. Combined with the UTC caveat, an agent has everything needed to call it and interpret the result 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?

Zero input parameters, so the baseline is 4. The description's discussion of `zone` concerns a returned field rather than an input, which adds useful meaning without misrepresenting the schema.

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 resource and scope: today's date on the athlete's Blocks account, in their own time zone, and even enumerates the returned components (ISO date, weekday, ISO week). It is clearly distinguishable from siblings like get_context or get_readiness_today.

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 states explicitly when to call it — to anchor relative reasoning ('today', 'tomorrow', 'this week', 'in 3 days') and to supply the correct `date` to other tools. This is direct routing guidance, not implied usage.

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