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

Annotations already declare the mutation profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), so the bar is lower. The description still contributes a real behavioral fact beyond them: logging does not disturb an active running timer, which matters for an agent mid-session. It omits edge cases such as overlapping existing entries or how the entry surfaces in summaries.

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 tight sentences with the primary definition first and the scoping caveat second. No redundant restatement of the title or schema.

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?

An output schema exists so return values need no explanation, and the schema fully covers parameters. The remaining gap is whether overlapping or duplicate entries are allowed and what validation failures occur (e.g. end before start), which an agent might want before committing a write.

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 coverage is 100%, so the schema already documents all four parameters including the flexible time formats and the activityId/activityName pair. The description only restates that a start and an end are required, adding nothing about choosing id versus name or about timezone defaults — correct baseline for schema-covered params.

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 verb and resource ('Record a finished block of time') and delimits scope ('not tracked live, with a start and an end'). The second sentence separates it cleanly from start_timer/stop_timer siblings, so an agent can pick it without opening the schema.

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?

'Was not tracked live' gives a clear condition for choosing this over live timer tools, and 'Does not affect a running timer' acts as an exclusion. It stops short of naming start_timer/stop_timer directly as the alternatives, so it is clear context rather than explicit routing.

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