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

Annotations already cover read-only/idempotent; description adds the exact formula, warns against MTBF/MTTF confusion, and instructs to quote verbatim, which is behavioral context beyond the structured flags. No contradiction found.

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 sentences, front-loaded with the formula and then rationale and usage. No redundant words.

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 tool is simple: two numeric inputs and a deterministic formula. The description provides the formula, usage conditions, and a caveat, making it fully self-contained despite no 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?

Both parameters are fully described in the schema (100% coverage), and the description only repeats the same-time-unit requirement, adding no new semantic detail. Baseline 3 is appropriate.

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 computation: availability = MTBF/(MTBF+MTTR) given the two parameters. It also contrasts with sibling explanatory tools by emphasizing it's a dedicated calculation tool.

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?

Explicitly says 'Use whenever a user supplies an MTBF/MTTR pair and asks for availability', giving a clear trigger. It doesn't list alternatives but the sibling set is mostly explanatory, so it's distinct.

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