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

Annotations already cover the write-safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), so the bar is lower. The description adds a real behavioral detail beyond them: started_at is auto-derived as now minus the duration when omitted.

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 short sentences, purpose front-loaded, example embedded, and the parameter default disclosed in the trailing clause. No filler.

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 an output schema present, return values need no explanation, and all four parameters are fully documented in the schema. The description covers purpose, an example, and the one non-obvious default, leaving little an agent would need to guess.

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%, so the baseline is 3; the description adds meaning beyond the schema by documenting the defaulting behavior of started_at (now minus duration). It also embeds an example mapping free-form input to key/minutes, which the schema does not.

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+resource ("Records time") and scopes it to time that "no timer measured", which conceptually separates it from start_timer/stop_timer siblings. It stops short of naming those siblings explicitly, so an agent must infer the boundary rather than read it.

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?

"Records time no timer measured" functions as an implied when-to-use/when-not condition, and the concrete example ("2h on APP-12 yesterday") shows the intended shape of a call. No alternative tool is named, so the routing is contextual rather than explicit.

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