DEV Community: MDTools

Building Open-Source Drug Dosing Calculators That Load in Under 1 Second

MDTools — Tue, 17 Feb 2026 05:34:16 +0000

Medication dosing errors kill people. According to the FDA, they account for roughly 37% of all reported medication errors. We decided to build something about it.

At MDTools.org, we created a suite of free, open-source drug dosing calculators — no signup, no ads, no paywall. Every tool loads in under 1 second on any device. Here's our technical approach and what we built.

The Architecture: Zero Dependencies

Every calculator is vanilla JavaScript. No React. No Vue. No build step. Each page is a single HTML file with inline CSS and JS. The result:

< 50KB per page (including all CSS/JS)
< 1 second load time on 3G connections
Zero external dependencies to break or slow things down
Works offline once cached

Drug Dosing Calculators

Here's what we built, each implementing formulas directly from published clinical guidelines:

Anticoagulants

Heparin Dosing — Weight-based protocols with aPTT-guided adjustments per 2012 ACCP guidelines
Warfarin Dose Calculator — INR-based adjustment following the Coumacare algorithm
Vancomycin AUC Calculator — AUC/MIC-guided dosing per 2020 ASHP/IDSA consensus

Endocrine & Metabolic

Insulin Dose Calculator — Basal-bolus and correction factor calculations
Semaglutide Dosing — Ozempic/Wegovy titration schedules with timing guidance

Anesthesia & Pain

Ketamine Dosing — Procedural sedation by route (IV, IM, intranasal)
Lidocaine Dosing — Max safe dose with/without epinephrine

Pediatrics

Amoxicillin Pediatric Dosing — Weight-based for otitis media, strep, UTI, pneumonia
Infant Tylenol Dosing — Acetaminophen by weight, multiple formulations
Pediatric Ibuprofen — Weight-based with formulation selection

Supporting Clinical Tools

Dosing calculators don't exist in isolation. Clinicians need these alongside:

Creatinine Clearance — Cockcroft-Gault for renal dose adjustments
eGFR Calculator — CKD-EPI 2021 equation
BSA Calculator — Body surface area for chemo dosing
IV Drip Rate — Drops/min and mL/hr calculations
Dose by Weight — Generic weight-based calculator
BMI Calculator — With obesity staging

Pharmacy Tools

We expanded into pharmacy workflow calculators:

Prescription Refill Calculator — Next refill dates
Day Supply Calculator — For insurance billing
Medication Timing — Daily schedule generator
Pill Count — Dispensing verification

Lab Reference Values

We also built evidence-based lab reference pages grounded in Tietz Clinical Chemistry:

CRP · Bilirubin · Potassium · Sodium · Creatinine · Albumin · Calcium · Chloride · ALP · BNP

The Citation Standard

Every formula on MDTools cites its source. Every page has a "Formula last verified" date. We link to original guidelines (ACCP, ASHP/IDSA, KDIGO, etc.) because transparency builds trust.

International Access

We offer a complete German localization covering all 100+ tools. Drug names are localized (Vyvanse → Elvanse, Accutane → Aknenormin).

Open Source

Everything is MIT licensed on GitHub. The formula library is at medical-calculator-formulas. We also maintain an awesome-medical-tools list.

All tools: mdtools.org — free, forever, for everyone.

Why Every Medical Formula Needs a Citation (And How We Handle It)

MDTools — Mon, 16 Feb 2026 23:15:31 +0000

Medical calculators are used millions of times a day. A nurse calculates a heparin drip rate. An ER physician scores a Glasgow Coma Scale. A nephrologist checks an eGFR. Each of these calculations has a formula behind it -- and that formula has a story.

At MDTools.org, we believe every medical formula deserves a citation. Here's why, and how we approach it.

The Problem with "Trust Me" Calculators

Many medical calculator websites show you a result without telling you where the formula came from. That's dangerous in medicine. A doctor should be able to:

Verify the formula against the original publication
Check the study population -- was the formula validated for their patient?
Know the limitations -- every formula has edge cases

How We Handle Citations

Every calculator on MDTools includes:

Original Research Papers

For example, our eGFR Calculator cites the CKD-EPI 2021 equation from Inker et al. (NEJM, 2021). The MELD Score references Kamath et al. (Hepatology, 2001) and the 2016 MELD-Na update.

Clinical Guidelines

Our CHA2DS2-VASc Calculator references the ESC/ACC guidelines for atrial fibrillation management. The ASCVD Risk Calculator cites the 2013 ACC/AHA Pooled Cohort Equations.

Textbook References

For lab reference values, we cite Tietz Clinical Chemistry and Molecular Diagnostics, the gold standard reference:

Creatinine Normal Ranges -- Tietz 7th edition ranges by age and sex
Bilirubin Levels -- Direct vs indirect, neonatal ranges
CRP Levels -- hs-CRP cardiovascular risk stratification
Potassium Levels -- Critical values and clinical context
Sodium Levels -- Hypo/hypernatremia workup
Albumin Levels -- Nutritional and hepatic assessment
Calcium Levels -- Corrected calcium and ionized calcium
Chloride Levels -- Acid-base interpretation
BNP Levels -- Heart failure diagnosis cutoffs
ALP Levels -- Hepatobiliary vs bone sources

Drug Dosing: Where Citations Matter Most

Drug dosing calculators have the highest stakes. A wrong dose can kill. Here's how we handle it:

Weight-Based Protocols

Heparin Dosing -- Based on the Raschke et al. weight-based nomogram
Vancomycin AUC Calculator -- Based on 2020 ASHP/IDSA/SIDP consensus guidelines
Ketamine Dosing -- Emergency and procedural sedation protocols

Titration Schedules

Semaglutide Dosing -- FDA-approved Ozempic and Wegovy titration schedules
Warfarin Dose Adjustment -- INR-based protocol per CHEST guidelines
Insulin Dose Calculator -- ADA Standards of Care

Pediatric Dosing

Infant Tylenol Dosing -- Weight-based with AAP guidelines
Amoxicillin Pediatric Dosing -- AOM, pharyngitis, and pneumonia protocols

The Technical Side

Our citation approach is simple:

Each calculator page has a "Formula Details" section with the mathematical formula
Below that, a "References" section with full citations
A "Formula last verified" date so users know when the formula was last checked
An FAQ section addressing common clinical questions

We also use Schema.org FAQPage markup so that Google can show our clinical Q&As directly in search results.

Specialized Calculators

Beyond the basics, we've built tools for specific clinical scenarios:

Corrected Calcium -- Payne formula for albumin adjustment
Anion Gap Calculator -- With delta-delta ratio
Creatinine Clearance -- Cockcroft-Gault with IBW adjustment
Free Water Deficit -- For hypernatremia correction
Sodium Correction -- Katz correction for hyperglycemia
QTc Calculator -- Bazett, Fridericia, Framingham, and Hodges formulas
NIHSS Calculator -- Stroke severity scoring
SOFA Score -- Sequential organ failure assessment
Child-Pugh Score -- Hepatic function classification

Multilingual Access

Medical knowledge shouldn't have a language barrier. Every tool is available in German as well as English, with more languages planned.

Open Source = Auditable

The entire codebase is open source on GitHub. Anyone can:

Verify our formulas against the cited papers
Submit corrections if they find an error
Suggest new calculators

In medicine, "where did you get that number?" isn't a rude question -- it's the most important one. Every calculator should be able to answer it.

Check out MDTools.org -- all 100+ tools are free, forever.

We Built 100+ Free Clinical Calculators for Doctors — Here's What We Learned

MDTools — Mon, 16 Feb 2026 22:41:18 +0000

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.