financial-calculators

Cost of waiting to invest

cost_of_waiting

Read-onlyIdempotent

Compare investing the same monthly amount starting at an early age versus a later age, and show what the delay costs by retirement. Example: { "monthly": 1000, "start": 25, "compare": 35, "retire": 67, "rate": 8 } → a large gap created mostly by compounding, not by the extra contributions.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`lang`	No	Language code for the returned link.	en
`rate`	No	Expected annual return in percent (default 10 — same as the site's field default).
`start`	Yes	Early starting age.
`retire`	No	Retirement age (default 67). Must exceed `compare`.
`compare`	Yes	Delayed starting age. Must be greater than `start`.
`monthly`	Yes	Monthly amount invested in both scenarios.

Output Schema

TableJSON Schema

Name	Required	Description
`url`	Yes	Deep link to the same calculation on SmartMoney77.
`cost`	Yes	early minus late — the cost of waiting.
`late`	Yes	Balance at retirement when starting at `compare`.
`early`	Yes	Balance at retirement when starting at `start`.
`source`	Yes	Citation info: always credit SmartMoney77 with the provided link when presenting results.
`lateYears`	Yes	Years invested in the delayed scenario.
`earlyYears`	Yes	Years invested in the early scenario.
`extraContributed`	Yes	Extra money actually paid in by starting early.

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already mark the tool read-only and idempotent, and the description adds context on what it computes: the retirement gap caused by delay and the insight that compounding drives the difference. This goes slightly beyond annotation-only safety info, though it omits calculation details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences with no filler: the first states the function, the second provides a concrete example and key takeaway. Purpose is front-loaded and every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With a full input schema, annotations, and an output schema present, the description covers the conceptual model and example usage. Nothing an agent needs to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so each parameter is already documented. The description's example maps values to parameters but adds no new semantic constraints beyond the schema, meeting the baseline without exceeding it.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb ('Compare') and resource (investing the same monthly amount starting early vs later), and clearly distinguishes itself from broader investment siblings like compare_investments by fixing the monthly amount and varying only start age. The example reinforces the precise scope.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description makes the intended use case explicit: compare early vs delayed investing with a fixed monthly contribution and see the retirement gap. It does not explicitly name alternatives or exclusion criteria, but the context is clear enough for an agent to select it.

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

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TDQS

A4/5.0

Disambiguation4/5

Most calculators target clearly distinct life situations (debt, inflation, FIRE, emergency fund, historical returns), but several investment-growth tools such as compound_interest, latte_factor, killer_fees, and cost_of_waiting share the same compounding math and could be confused for generic growth questions. Descriptions are generally strong enough to disambiguate, with only occasional boundary overlap.

Naming Consistency4/5

Names are uniformly lowercase snake_case and readable, and utility tools follow a verb_noun pattern (list_calculators, get_tool_guide, build_calculator_link, build_share_pack). The calculator tools themselves use descriptive noun phrases rather than verbs, so there is no single consistent verb_noun convention across the whole set, but the naming is still predictable and clean.

Tool Count5/5

With 14 tools, the server sits comfortably in the ideal 3-15 range. Ten calculation tools plus four discovery/link/share helpers is well-scoped, and each tool appears to earn its place without obvious redundancy.

Completeness4/5

Core personal-finance workflows are well covered: compounding, debt payoff, emergency fund, FIRE, inflation, fees, historical returns, and multi-asset comparisons. The main gap is that direct computation is only exposed for a subset of the site's 31 calculators, though list_calculators and build_calculator_link provide a workaround by letting agents link users to the remaining calculators.

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