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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint. The description adds value by stating 'Every call is read-only and idempotent', 'never raises a protocol error', returns an error object, and includes disclaimers like 'FREE' and 'not financial advice'. No contradictions with annotations.

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?

The description is fairly concise, front-loading the main purpose. All sentences are informative and avoid redundancy. It could be slightly more structured, but overall it is efficient and clear.

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, the description need not explain return values. It covers error handling, idempotency, read-only nature, usage guidance, sibling differentiation, and includes an example. The description is complete for a tool of this complexity.

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?

The input schema has 100% description coverage, so baseline is 3. The description includes a typical input example but does not add new semantic details beyond the schema's parameter descriptions. It meets the baseline but does not go significantly beyond.

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 starts with a specific verb+resource: 'Compute months to reach a savings target at a monthly contribution.' It clearly distinguishes from siblings by stating that it is not for budget_split or loan_payment, making the purpose unambiguous.

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 ('Use when a target amount and a monthly contribution are known'), provides exclusions ('Not for allocating income across categories... not for loan repayment'), and mentions that the tool is safe to retry after errors, guiding the agent on correct invocation.

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