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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so safety is covered. The description adds genuinely useful framing beyond that: it states results are estimates and not financial advice, and it spells out computed defaults (fat at 150% of spending, lean at 75%) and the required inputs. It does not describe the shape of the returned numbers, which is the main residual gap.

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?

Sentences are front-loaded and each variant clause earns its place by encoding a distinct routing rule. There is mild keyword redundancy ('coast FIRE calculator, barista FIRE calculator or FIRE number calculator') that could be trimmed without losing information.

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 11-parameter calculator with no output schema, the description supplies what the agent most needs: required inputs, defaults for the optional ones, per-variant intent, and the estimate/not-advice caveat. It stops short of saying what the response contains (per-variant numbers, currency display), leaving a small gap for a multi-output calculator.

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 all 11 parameters including enums, defaults and bounds are already documented. The description only restates the required inputs and the optional monthly investing and target age, without adding format or interaction details beyond the schema — the baseline 3 applies.

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 names a concrete deliverable (a FIRE number for lean, fat, coast or barista variants) and ties each variant to the user's intent. It also explicitly contrasts itself with the sibling retire_at_age, so an agent can route without opening either 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?

It gives per-variant activation cues ('Use coast when...', 'Use barista when...', 'Use lean when...', 'Use fat when...') plus explicit exclusions (retire-at-age checks, job/salary advice, tax, investment picking) and names the alternative tool. This is the full when/when-not/alternatives pattern.

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