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

Beyond the annotations (non-readonly, non-idempotent, non-destructive), the description discloses the critical side effect: only one timer can be active per person and starting a new one stops the old one. It even describes what the response reports (which timer was stopped and how many minutes it logged), which is real behavioral context the annotations cannot convey.

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?

Purpose is front-loaded in the first clause, followed by side effects and the alternative tool. The sentence about stopping the previous timer is slightly convoluted in phrasing but every sentence carries distinct, necessary information; nothing is redundant.

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 2-parameter mutation tool with no output schema, the description covers the action, the single-active-timer constraint, the stopping behavior, the return content, the billable default, and the log_time alternative. An agent has everything needed 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 coverage is 50%: issueId is richly documented in the schema, while billable has no schema description. The description compensates by defining billable's default (true) and its business meaning (set false for internal work not billed to the client), so both parameters are usable. It stops short of explaining issueId, but the schema already covers it well.

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?

"Arranca TU reloj en una issue" is a concrete verb+resource, and the description immediately distinguishes this from log_time (for work already done) and implicitly from stop_timer. An agent knows exactly what this tool does and what it is not before 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?

It gives an explicit rule: use start_timer for live tracking, use log_time when the work is already finished and no clock is needed. It also tells the agent that starting a timer while another runs will stop the previous one, which is the key decision-relevant precondition.

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