Methodology

Source of truth

Every formula, score, or conversion is implemented from its original paper, guideline, or specification. Examples:

• Cockcroft & Gault (1976), Nephron
• CKD-EPI 2021 race-free creatinine equation (Inker et al., NEJM)
• MELD / MELD-Na (Kamath et al., Hepatology)
• Sepsis-3 SOFA / qSOFA (Singer et al., 2016, JAMA)
• APACHE II (Knaus et al., 1985, Crit Care Med)
• NCEP ATP III Framingham tables
• JWT — RFC 7519, Web Crypto API for verification
• Base64 — RFC 4648

References appear on every tool page so the citation is one click away. Where a DOI or PubMed link exists, the citation is hyperlinked.

Testing

The pure math behind each calculator lives in a tiny JavaScript module (e.g. src/tools/health/cha2ds2-vasc.js). Each module has a sibling *.test.js file run by Vitest in CI. Tests check the formula against worked examples from the original paper or a recognised reference (MDCalc, ClinCalc, AHA pocket cards). For purely categorical scores, we cross-validate against a second well-known source.

As of the last audit run, the test suite contains 860+ tests and runs in under 5 seconds. Any pull request that breaks a test cannot merge.

What is intentionally not shipped

Some tools that are commonly requested are not implemented, on purpose, because we can’t implement them correctly today. An inaccurate calculator is worse than no calculator. The current "no-ship" list:

• EuroSCORE II — requires the full proprietary regression coefficients.
• AHA/ACC PREVENT equations — superseded model, not yet available with the official coefficient tables.
• Pediatric BMI and BP percentile tables — require the WHO/CDC LMS reference tables; reproducing them needs careful per-age interpolation.
• Disease-specific decision algorithms that change per institution (e.g. local sepsis protocols).

When we ship one of these in the future, the page will say "added because we now have access to authoritative coefficients" with a citation.

Updates and versioning

Clinical guidelines change. When a guideline supersedes a previous one, we ship a new tool at a new URL and link from the old one (e.g. CHADS₂ → CHA₂DS₂-VASc; MDRD → CKD-EPI 2021). We do not silently overwrite the math on an existing URL — that would change the answer for anyone with the page bookmarked or cited.

Privacy in tool design

Every tool runs in the browser. No tool input is ever sent to a server. We use this constraint as a design rule, not just a policy claim — it is enforced by the fact that the site has no backend that could receive tool input.

Reviewer status

maratool currently has no licensed clinical reviewer of record. Tools are built and maintained by Marcell Almeida (software engineer). We disclose this openly on the medical disclaimer page rather than implying credentials we don’t have. If you are a clinician interested in reviewing specific tools, please get in touch.

Reporting issues

If a formula doesn’t match its source, an interpretation band disagrees with current guidelines, a unit conversion is wrong, or a calculator throws unexpected output: email maratool@marcell.com.br. These are treated as priority bug reports.