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

Annotations already declare destructiveHint=true and idempotentHint=true; the description adds real context beyond them by stating no time is logged and that the call is refused when no timer is running. That precondition/error behavior is exactly the kind of detail annotations cannot carry, though permissions or post-cancel state are not addressed.

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 compact sentences: what it does, then the analogy and the refusal condition. The distinguishing fact (no time logged) is front-loaded and nothing is padded.

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 not be described, and the one optional parameter is fully covered by the schema. The description supplies the missing behavioral piece (no time logged, refusal when idle), leaving nothing an agent needs to invoke it 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 100% and the single userId parameter is already fully documented as optional and only relevant to workspace connections. The phrase 'the signed-in person's running timer' reinforces the same default scoping, but adds no syntax or format detail beyond the schema — baseline 3.

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?

Specific verb ('Discards') plus resource ('the signed-in person's running timer') with an explicit scoping clause ('without logging any time') that separates it from stop_timer at a glance. The agent can distinguish this from start_timer/stop_timer/list_running_timer without opening any 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?

Frames the tool as 'the undo for starting one by mistake', giving a clear condition for choosing it, and the 'without logging any time' clause implicitly steers away from stop_timer. It stops short of naming stop_timer as the alternative, so the routing is inferred rather than spelled out.

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