Every day, doctors around the world calculate drug doses, interpret lab values, and score clinical assessments. Most of these calculations happen on paper, in someone's head, or on outdated websites buried behind paywalls and registration walls.
We thought that was wrong. So we built MDTools.org -- a completely free, open-source collection of 100+ clinical calculators.
Why We Built This
The dominant player in medical calculators charges institutions for API access and locks certain features behind registration. We wanted something different:
- Free forever -- no freemium, no subscription tiers
- No login required -- doctors are busy, don't make them create accounts
- No ads -- clinical tools shouldn't have banner ads for pharmaceuticals
- Open source -- anyone can audit the formulas, suggest corrections, or fork the project
- Fast -- static HTML + vanilla JS on Cloudflare Pages, loads in under 1 second globally
What's Under the Hood
The entire site is vanilla HTML, CSS, and JavaScript. No React, no build step, no npm dependencies in production.
Each calculator is a single HTML file with:
- Structured data (Schema.org JSON-LD) for SEO
- Evidence-based formulas with citations
- Mobile-responsive design
- Accessible form inputs
Architecture
mdtools.org/
index.html # Homepage with search + category filters
bmi.html # BMI Calculator
gfr.html # eGFR (CKD-EPI 2021)
a1c.html # A1C to average glucose
gcs.html # Glasgow Coma Scale
meld.html # MELD-Na Score
styles.css # Single shared stylesheet
region.js # Auto-detect language
de/ # Full German translation (113 pages)
No bundler. No framework. Just files served from a CDN.
The Calculators
Here are some of the most-used tools:
Core Clinical
- Glasgow Coma Scale (GCS) -- Neurological assessment
- MELD-Na Score -- Liver transplant prioritization
- CHA2DS2-VASc -- Atrial fibrillation stroke risk
- APACHE II -- ICU mortality prediction
- SOFA Score -- Organ failure assessment
Kidney & Electrolytes
- eGFR Calculator (CKD-EPI 2021) -- The gold standard
- Creatinine Clearance -- Cockcroft-Gault
- Corrected Calcium -- Albumin adjustment
- Anion Gap -- Metabolic acidosis workup
- Sodium Correction -- For hyperglycemia
Metabolic & Nutrition
- A1C Calculator -- HbA1c to estimated average glucose
- BMI Calculator -- With WHO classification
- TDEE Calculator -- Total daily energy expenditure
- Body Fat Calculator -- US Navy method
Drug Dosing
- Semaglutide Dosing -- Ozempic/Wegovy titration
- Heparin Dosing -- Weight-based protocol
- Vancomycin AUC -- 2020 guidelines
- Warfarin Dose -- INR-based adjustment
Lab Reference Values
- Bilirubin Normal Range -- With clinical context
- CRP Levels -- Inflammation marker
- Potassium Levels -- Critical values explained
- Creatinine Levels -- Kidney function basics
Lessons Learned
1. Vanilla JS is underrated
For calculators, you don't need React. Each page is a self-contained form with an event listener. The entire site weighs less than most framework bundles.
2. SEO matters more than you think
Medical professionals actually Google things like "GFR calculator" and "MELD score calculator". Getting the structured data right (BreadcrumbList, FAQPage schema) has been crucial for visibility.
3. Doctors want simple, fast tools
No one wants to create an account to calculate a creatinine clearance. The simpler the UX, the better.
4. Citations matter in medicine
Every formula includes references to the original research papers. Medical professionals need to trust the source.
5. Internationalization opens doors
We built a full German version at mdtools.org/de/ and are exploring other languages. Medical knowledge shouldn't have a language barrier.
Open Source
The entire project is open source on GitHub: github.com/computerdude11111/mdtools
Contributions welcome -- whether it's:
- New calculator ideas
- Formula corrections
- Translations
- UX improvements
What's Next
- More lab reference pages (we're building a comprehensive library)
- Additional languages beyond English and German
- A DICOM viewer (already live at mdtools.org/dicom)
- Browser extension for quick access
If you're a developer interested in healthcare, there's a lot of low-hanging fruit in medical tools. The barrier isn't technical -- it's understanding what clinicians actually need.
Check out MDTools.org and let us know what you think. Every tool is free, forever.
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