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

With all annotations set to false, the description carries the full burden of behavioral disclosure. It adds a key non-obvious behavior: starting a new timer stops and logs the previous one. This goes beyond the schema and gives the agent important side-effect information.

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?

The description is two sentences, tightly written, with the primary purpose front-loaded. Every sentence contributes meaning: purpose, behavior, and a key parameter clarification. No redundancy or filler.

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?

The description covers the core behavior, the single-run constraint, and the return value (start time). It does not detail error handling or the exact naming convention for the logged previous timer, but these are secondary. Given the schema covers parameter specifics, the description is adequate for an agent to invoke the tool 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 100%, so the schema already documents all parameters. The description adds only a clarification about 'MAJOR units' for the rate parameter, which is useful but minimal. It does not elaborate on tags, task, currency, or project beyond what the schema provides.

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 clearly states a specific action: starting a stopwatch for project work and returning the start time. It also distinguishes itself from siblings by noting that only one timer runs at a time, implying this tool supersedes any existing timer.

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 implies when to use it (to start a timer) and notes that it stops the previous one, but it does not explicitly mention alternatives like timer_stop for stopping without starting, or when not to use this tool. The guidance is implicit rather than explicit.

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