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

Annotations already declare readOnlyHint, idempotentHint, and a closed world, so the safety profile is covered. The description adds genuinely useful output context — it returns which digits are significant plus 'the rule behind each one' — which is behavior beyond the structured fields.

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 tight sentences plus a URL, and the hook question is front-loaded before the capability statement. Slightly padded by the trailing web-page link, but nothing is wasted.

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 read-only, zero-required-param calculator with full schema coverage and no output schema, the description tells the agent what it computes and what it returns. Adequate, though it could mention result format expectations more explicitly.

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 description coverage is 100%, so the schema already documents 'number' (trailing zeros matter, scientific notation) and 'round'. The description only restates rounding to 'as many as you need' and reinforces the example, adding little beyond what the schema provides; baseline 3 applies.

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 (identify which digits are significant, then round) and resource (an input number), and the opening example ('Does 0.004050 have 3 or 4 sig figs?') concretely fixes the scope. This is clearly distinct from adjacent math siblings like scientific_notation_converter or exponent_calculator.

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?

'Paste any number... then round it to as many as you need' implies the workflow, but the description never names when to prefer this over a sibling (e.g. scientific_notation_converter) or any exclusions. Usage is inferable rather than stated.

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