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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds value beyond them: it discloses the error contract (returns {"error": ...} rather than raising a protocol error, with a sample message), asserts retry safety after correction, and flags it as administrative math rather than advice. This is exactly the context annotations cannot express.

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?

Well front-loaded — the one-line purpose and FREE badge come first, then the example, then usage and error behavior. The example return value is largely redundant given an output schema exists, which is the only real slack in an otherwise tight definition.

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 3-param pure-computation tool with full schema coverage, annotations, and an output schema, the description covers everything left: when to use, what it is not, compounding behavior, and the error/retry contract. An agent can call it correctly from this alone.

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 earns extra by giving a worked example ({target: 10000, monthly_saving: 400, annual_rate_pct: 4}) and stating that interest compounds monthly, showing how the parameters interact rather than just restating their definitions.

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+resource+scope: 'Compute months to reach a savings target at a monthly contribution', and immediately disambiguates from budget_split and loan_payment. The concrete example input/output makes the computation unambiguous without opening the schema.

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 states when to use ('when a target amount and a monthly contribution are known') and names two exclusions with the sibling responsible for each (budget_split, loan_payment). Nothing is left to inference.

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