Start timer

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

No annotations are provided, so the description carries the burden; it discloses the key side effect: only one timer runs and starting a new one stops and logs the previous one. It does not elaborate on output or persistence beyond that, but the core behavioral trap is explicitly flagged.

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 sentences with no filler. The first sentence front-loads action and scope; the second delivers the most important behavioral caveat.

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 simple state-transition tool with fully described schema parameters, the description captures purpose and the critical runtime constraint. It does not describe return values, but no output schema exists and the endpoint's behavior is adequately specified for selecting and invoking 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 input schema covers all 5 parameters with their own descriptions, so the description does not need to repeat those semantics. It adds 'project or client' context but leaves rate, tags, and currency details to the schema, which is appropriate at full schema coverage.

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 action ('Start a stopwatch') and resource scope ('billable work on a project or client'), and the single-timer limitation distinguishes it from siblings like timer_stop and timer_status. The title and name are expanded, not merely echoed.

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?

Clear context: use when beginning billable tracking for a project or client. It does not explicitly name alternatives or exclusions, so it stops short of the top score.

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