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

The annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered. The description adds that four time windows are computed, which is mildly useful context, but says nothing about precision, rounding, or edge cases for out-of-range percentages.

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 sentences, with the triggering user question front-loaded before the functional summary. Every clause carries information and there is no padding.

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 one-parameter, pure-computation tool with an output schema and full annotation coverage, the description supplies everything an agent needs to decide to call it and what to pass. Return-value details are correctly delegated to the output schema.

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?

With a single parameter and 100% schema description coverage, the schema already documents availability_pct including its format ("e.g. 99.9 for three nines"). The description's "like 99.9% or 99.99%" merely echoes that format, adding no new semantics such as valid bounds.

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 — converting an availability SLA percentage into downtime budgets — with the scope of outputs enumerated (annual, monthly, weekly, daily). This is clearly distinguishable from sibling calculators like error-budget-calculator or slo-burn-rate-calculator, though no sibling is named explicitly.

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?

"Use this when a user asks what a specific availability percentage (like 99.9% or 99.99%) means in downtime minutes per month or year" gives an explicit, concrete trigger condition. There is no when-not guidance and no named alternative tool for adjacent questions, which keeps it short of a 5.

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