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

Annotations already declare this a destructive, non-idempotent write. The description goes beyond them by disambiguating focus=none (hands the date back to the coach) from focus=null (clears), and by stating the 'only one weekday can be the long run' constraint. It still doesn't spell out what existing entries are overwritten.

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-loads the core purpose in the first clause and follows with two tight clarifying sentences. The none/null clause is dense but earns its place; little 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 3-parameter destructive mutation with no output schema, the description covers both operating modes, the key enum edge cases, and a validation constraint. It leaves minor gaps (overwrite semantics, permission needs) but is largely sufficient to call 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 only 33% (only today is documented), so the description must compensate. It explains what days and weekly each set and clarifies the subtle none-vs-null distinction for focus, adding real meaning the schema leaves silent.

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 (Sets) and resource (a coming day's focus, or a weekday's recurring focus), and cleanly splits the two modes by naming the days and weekly parameters. It does not, however, differentiate itself from the sibling schedule tool, which an agent could easily confuse it with.

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?

The days-vs-weekly split implicitly tells the agent which parameter to reach for in which scenario, and the none/null note gives conditional behavior. But there is no explicit when-to-use vs the sibling schedule tool, no prerequisites, and no stated exclusions.

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