Methodology
How a tool gets from "we should build this" to "live on the site." Same process for every tool, regardless of category.
Sourcing the formula
Every tool starts from a citable source. For tax and payroll tools, the source is the relevant IRS publication, FLSA section, or state labor code. For construction tools, it is the relevant section of the IBC or the trade-standard reference (lumber: NDS; HVAC: ASHRAE Manual J; concrete: ACI). For finance tools, it is the standard formula from a peer-reviewed or textbook source.
The source is named in the tool's "How it works" section. If the source is an external standard with a stable URL (an IRS publication, for example), the tool links to it.
Implementing the calculation
Tools are implemented as small, pure functions. Each function takes structured inputs and returns a structured result. Functions live in their own files and are unit-tested with a test suite that runs in continuous integration.
When the underlying formula has well-known edge cases (negative inputs, unit conversions, rounding behavior, tax bracket boundaries), the test suite includes those edge cases explicitly.
Validation against a known tool
Before a tool ships, we run a fixed set of test inputs through both our implementation and an independent reference (a published example in the source document, an existing well-regarded tool, or a manual calculation done with the original formula). The results must match within an acceptable tolerance for the domain.
Editorial review
A reviewer separate from the implementer reads the tool page end to end: the calculation, the explanation, the worked examples, the FAQ. The reviewer checks that explanations are accurate, that examples produce the stated results, and that no claim exceeds what the formula supports.
Review cycle
Every tool has a "last reviewed" date in its byline. Tools are reviewed again at least every twelve months. Tools that depend on regulations which change (tax brackets, FLSA rules, building codes) are reviewed when the regulation changes, regardless of the twelve-month cycle.
Corrections
When a reader reports an error and the report is correct, we fix the tool, update the last-reviewed date, and note the change in the editorial changelog. See editorial standards for the corrections policy in detail.