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

Beyond the annotations, the description explains the actual effects: it logs the timer as one entry, returns duration, money, and the new entry id, and does nothing if no timer is running. This gives the agent a solid understanding of side effects and edge-case behavior.

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?

Three short sentences front-load the core action, then cover return values and the no-timer behavior. There is no filler or redundant information.

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 tool with one optional parameter and no output schema, the description covers the main scenario, the return values, and the edge case where no timer is running. Nothing material is missing for an agent 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?

The input schema already documents the optional 'note' parameter with 100% coverage. The description does not add any extra meaning about the parameter, so it meets the baseline but provides no additional value here.

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?

The description states a specific verb ('Stop'), a precise resource ('the running timer'), and the resulting action ('log it as one entry'). It also mentions the new entry id, which clearly separates it from sibling tools like timer_start, timer_status, and entry_add.

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?

The description clearly implies when to use this tool: when a timer is running and should be stopped and logged. It also covers the no-timer case by saying it writes nothing, but it does not explicitly name alternatives such as timer_start or timer_status.

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