focus_today

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

No annotations are supplied, so the description carries the full burden. It does disclose a non-obvious constraint (requires app 3.8+) and enumerates the returned metrics, which is genuine added context. It never states that the tool is read-only or what happens on older app versions, leaving the mutation/safety profile inferential.

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 front-loaded sentence with the version constraint in parentheses and the returned fields listed compactly. No filler, no redundancy, nothing that could be cut.

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 zero-parameter read tool with no output schema, the description supplies the returned shape and a version caveat, which is close to sufficient. The only real gap is the absence of any read-only/safety statement given that no annotations exist to cover it.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The enumeration of returned fields is a bonus rather than a substitute for missing parameter info.

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 concrete resource (today's focus statistics) and enumerates exactly what it covers: session rounds, total minutes, and per-todo minute breakdowns. This is much more than a restatement of the name. It does not, however, distinguish itself from siblings like today_summary or water_today, so an agent must infer the boundary from the noun alone.

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 by the word 'today' and the stats framing — an agent can reasonably infer this is for reading focus data for the current day. There is no explicit when-to-use condition, no mention of when to prefer today_summary instead, and no stated prerequisites beyond the app version.

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