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

Annotations already declare this is a non-destructive, idempotent mutation, so the safety profile is covered. The description adds one genuinely useful behavioral fact beyond them — 'the time so far stays on it' tells the agent accumulated elapsed time is preserved. It does not state behavior when the stopwatch is already paused, whether the caller can pause another user's stopwatch, or any error conditions.

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 short sentence, front-loaded with the action, with the only non-obvious fact (time retained) appended. No filler, no restating of the title.

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 one-parameter, non-destructive, idempotent mutation with a fully documented schema and no output schema, this is nearly sufficient. The remaining gap is edge-case behavior (already paused, ownership scope), which the idempotentHint partly covers.

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?

Single required parameter with 100% schema coverage; the schema description 'From list_stopwatches' even routes the agent to the correct discovery tool. The description adds no parameter-level meaning, which is acceptable at this coverage level but is baseline, not value-add.

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 (pauses) plus resource (stopwatch) with the added scope 'one of the user's stopwatches.' It is clearly distinguishable from start_stopwatch/resume_stopwatch/discard_stopwatch by the verb, though it never names those siblings explicitly.

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 implied — you pause a stopwatch that is currently running — but there is no explicit when-to-use, when-not-to-use, or pointer to resume_stopwatch/start_stopwatch as the inverse operation. The agent must infer the routing from sibling names alone.

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