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

Annotations already declare a read-only, idempotent, non-destructive computation, and the description goes further by disclosing how the output changes with input: baseline amount needed plus 4%/3.5%/3.3% withdrawal-rate variants, and with optional inputs added, the age reached, shortfall or surplus, and extra monthly amount required. It also sets the expectation that results are an estimate, not financial advice, which is useful framing for how an agent should present the numbers.

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?

It is front-loaded with the usage trigger and then moves to inputs and output behavior in a logical order. The long list of example phrasings is slightly dense but each cluster maps to a real query pattern, so little is wasted.

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 no output schema and nine parameters, the description carries the burden of explaining results and does so for both the minimal and enriched invocation modes. Combined with the currency coverage note and the scope exclusions, an agent has everything needed to call it and interpret the answer.

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 per-field meaning is already documented and the baseline is 3. The description adds cross-parameter semantics the schema cannot: spending must be monthly or yearly, target age is mandatory, and age/netWorth/monthlyInvestment are optional but unlock additional computed outputs, which tells the agent how to decide whether to supply them.

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 specific tool type (retirement calculator) scoped to a chosen target age and anchors it with concrete user phrasings like "can I retire at 50 with $500k" and "the 25x rule / 4% rule". It also explicitly distinguishes itself from calculate_freedom_day for the open-ended age question, so an agent can route correctly 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 explicit when-to-use triggers (age-specific retirement questions, 4%/25x rule) and explicit when-not-to-use cases (open "when can I retire" with no age, pension/Social Security/annuity rules, tax, investment selection), naming the alternative tool for the excluded case. 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.