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

The annotations already declare this as read-only, idempotent, non-destructive, and closed-world. The description adds useful behavioral context beyond that: it explains the real after-inflation return assumption, the 7% default, and that current savings and monthly contributions are used to show the gap and Coast FIRE age.

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 front-loaded with the usage condition and examples, then moves efficiently into the calculation concept and assumptions. Every sentence contributes to selecting or correctly interpreting the calculator.

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 an 8-parameter calculator with full schema coverage and no output schema, the description is complete enough: it explains the key outputs (gap and age reaching Coast FIRE), the return assumption, and the relationship between spending, withdrawal rate, and FIRE number. Remaining details such as parameter bounds and defaults are already covered by the 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?

Schema description coverage is 100%, so the baseline is 3. The description adds meaning by explaining the relationship between annual spending, withdrawal rate, and the FIRE number, and by clarifying that current savings and monthly contributions drive the gap and age calculation.

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 calculation and resource: it computes the FIRE number, Coast FIRE number, gap, and the age Coast FIRE is reached. It distinguishes Coast FIRE from ordinary FIRE by defining it as 'what you need invested now so growth alone reaches your FIRE number by retirement age,' so an agent can tell what this tool uniquely does.

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?

It gives clear triggering guidance with example user questions such as 'what is my Coast FIRE number at 30?' and 'can I stop saving for retirement and let it grow?'. It does not explicitly route plain FIRE-number questions to the sibling calculate_fire_number tool, so the alternative-selection guidance is not fully complete.

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