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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely non-structured behavior: the test is timed, word content comes from the website's English word list, and metrics (WPM, accuracy, errors) are reported only at expiry — which tells the agent the call is asynchronous in effect.

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?

Two front-loaded sentences with no filler; the duration range and the reported metrics both earn their place. The phrase "returns its words" is slightly awkward and could be read as a return value rather than the test's word source, a small clarity cost.

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?

With an output schema present, return values need not be explained, and the description still summarizes the reported metrics. Together with full schema coverage and annotations, an agent has enough to invoke it correctly; only the `text` option and any timing/expiry mechanics of the result are left implicit.

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 baseline is 3. The description reinforces the duration values (30/60/120) but says nothing about the `text` parameter (words/punctuation/numbers), leaving that entirely to the schema; no syntax or default behavior is added beyond structured data.

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 and resource ("Starts a timed typing test") and scopes it to 30/60/120 seconds with words drawn from the site's English word list. It is unambiguous what the tool does, though it never differentiates itself from siblings — a mild gap given siblings like open_keyboard_tester are adjacent in domain.

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 only implied: the agent learns the tool starts a timer and that results appear "when time is up," which suggests when it is appropriate. There is no explicit when-to-use/when-not guidance or named alternative (e.g., versus open_keyboard_tester), so an agent must infer the choice.

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