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

Goes well beyond the annotations by disclosing the real side effects: the one-timer-per-person rule, that a running timer is stopped and its time kept first, that sub-30-second runs are discarded as accidental clicks, and that hours are rounded to the minute and capped at 16 hours. This is exactly the mutation context an agent needs, and it is consistent with destructiveHint=true.

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?

Four tight sentences, front-loaded with the action before the behavioral rules and the permission requirement. Every sentence carries distinct, call-relevant information with no padding.

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 mutation tool with no output schema, the description covers the mutation semantics, the side effects on existing timers, the rounding/cap rules, and the required role. Nothing an agent needs to call it correctly is missing.

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 defines note, cardId, and boardId, putting the baseline at 3. The description adds relational meaning by stating the timer runs on a project and optionally on one of its tasks, reinforcing that boardId is optional when cardId is supplied.

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 and resource ('Starts the user's time tracker on a project, optionally on one of its tasks'), with scope precise enough to distinguish it from stop_timer, get_running_timer, and log_time among the siblings. No ambiguity about what the tool does.

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?

Gives the precondition needed to invoke it (editor role on the project) and clarifies the project/card relationship, which effectively tells the agent when this tool applies. It stops short of explicitly naming alternatives such as log_time for manual entries or stop_timer, so it is clear context rather than full when/when-not guidance.

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