The Problem

I’ve been diving since 1993 and instructing since 2009. I did my first technical diving course in 2013, and ten years later — in February 2023 — I became a technical diving instructor. In all that time, I’ve used the main planning tools on the market. They work. MultiDeco, V-Planner — they do the job.

So why build another one?

Three reasons. The first is understanding. I didn’t just want to use a decompression planner — I wanted to know what was happening inside the numbers I was trusting my life to. Not just which buttons to press, but why those buttons produce those numbers and what happens when conditions change.

The second is education. When I started teaching technical diving, I wanted to improve on the available teaching materials. I was supplementing courses with YouTube videos and improvised diagrams to explain decompression theory to students. I wanted something interactive — something that showed the theory, not just stated it. That became the Deco for Dummies section of DiveToolKit.

The third is that the existing tools come with baggage — per-platform licensing, closed ecosystems, and in one case a creator whose behaviour underwater I wouldn’t want to endorse. I wanted something free, open, and web-based. Something a student could pull up on any device without paying three times for the same product — and where a plan you build on your computer is right there on your phone when you get to the dive site.

So I built my own.

What DiveToolKit Does

DiveToolKit is a single tool that handles the complete technical diving workflow — from gas blending to dive planning to decompression scheduling.

Gas Blending. You tell it what mix you need, what’s already in your tank, and what gases you have available. It gives you a step-by-step fill plan using partial pressure blending — the method every serious gas blender uses. Nitrox, trimix, heliox — whatever the dive calls for.

Decompression Planning. Full Bühlmann ZHL-16C with adjustable gradient factors — the same algorithm running inside most modern dive computers, implemented properly. Multi-gas planning with up to six gases, including deco switches. You get a complete runtime table you can take to the water.

Quick Calculations. MOD, END, EAD, best mix, gas density, SAC rate — all the numbers a technical diver checks before every dive, in one place. No switching between apps. No re-entering your settings each time.

Education. A built-in section that explains the science — Dalton’s Law, how the Bühlmann algorithm works, what gradient factors actually do, how oxygen toxicity accumulates. Because understanding why the numbers matter is what separates a diver who follows a plan from a diver who can adapt when the plan changes.

Why It’s Free

Let me be direct about this.

I could charge for DiveToolKit. The established competitors charge $30 to $50. Some have moved to subscription models — pay monthly for the privilege of planning your dives safely. I find that uncomfortable. Safety tools shouldn’t have a paywall.

DiveToolKit is free because its purpose isn’t to generate app revenue. Its purpose is to make technical diving safer and more accessible — and to demonstrate what Blue Ribbon Dive Resort stands for.

We’re an SDI/TDI 5-Star Dive Centre. We train technical divers. We believe that the tools of technical diving — the knowledge, the calculations, the planning methodology — should be available to every diver, not just those willing to pay for premium software. When a diver uses DiveToolKit to plan a dive, learns something from the educational section, and then thinks “I’d like to do a tech course with the people who built this” — that’s the business model. Not a subscription fee.

The technical diving market is small. App revenue from a niche within a niche is modest. A single multi-day technical diving course at Blue Ribbon — with gas fills, accommodation, and instruction — is worth more than thousands of app downloads at $5 each. So the app is free, the value is in the diving, and the tool speaks for itself.

Why I Built It Myself

I wanted to understand what was happening inside my dive computer.

That’s the real answer. As a technical diving instructor, I trust my life to an algorithm running on a wrist-mounted device — and for years, I didn’t truly understand the maths behind it. I knew that it worked. I knew the gradient factors I preferred. I knew when to trust it and when to add conservatism. But I didn’t know why. And that bothered me.

So I went back to the source. Haldane’s original decompression research from 1908. Bühlmann’s work on the ZHL-16 algorithm. The actual papers, the actual equations, the actual tissue compartment coefficients. Not a textbook summary — the primary sources.

The only way to truly understand a decompression algorithm is to build one. So I did. What started as a learning exercise — can I implement Bühlmann ZHL-16C correctly and get it to match the published reference values? — turned into a tool I actually wanted to use. And once I had a working decompression planner, it made sense to add the gas blending calculator, the quick-reference tools, the educational content. A year later, DiveToolKit was a complete technical diving toolkit.

There were practical frustrations too. The established planning tools charge per device — buy it on your phone, buy it again on your tablet, buy it again on your PC. I’d paid for the same product three times. That licensing model made sense in the desktop era. It doesn’t make sense when a diver might plan on their laptop at home, check on their phone at the dive site, and review on a tablet in the evening.

And then there’s the personal angle. The creator of the most widely-used decompression software once dived with us here at Blue Ribbon. On that dive, he ran low on air, refused to ascend, and tried to breathe his girlfriend’s gas supply — then got aggressive with the divemaster and me when we insisted he surface. We ended up kicking him out of the resort. I’ll leave the name out of this, but let’s just say it became difficult to keep paying for his software after that. Sometimes the motivation to build your own tools is as simple as not wanting to give money to someone who doesn’t follow the safety principles his own software is supposed to protect.

DiveToolKit is a web app. It runs on anything with a browser. One tool, every device, no additional licenses. Log in on any device and your settings, gas mixes, and dive plans are all there — plan on your computer at home, pull up the same plan on your phone at the dive site.

But the core motivation was always the understanding. Every calculation in DiveToolKit is transparent — the maths is visible, the algorithm is documented, the reference values are cited. If you want to verify that the decompression schedule is correct, you can trace every number back to Bühlmann’s original work. Because when you’re planning a dive to 60 metres with mandatory decompression stops, “trust me” isn’t good enough. You should be able to see exactly what the tool is doing and why.

What’s Coming

DiveToolKit is a web app today — it runs in your browser, works offline, and looks clean on a phone. A native mobile app is in development for iOS and Android, with the same calculation engine underneath.

If you’re a technical diver, try it. If you’re considering getting into technical diving, use the educational section to understand what you’re getting into before you sign up for a course. And if you’re planning a trip to Anilao — we’d love to show you the sites in person.

Jonathan Venn is an SDI/TDI Instructor Trainer and the owner of Blue Ribbon Dive Resort in Anilao, Mabini, Batangas — the birthplace of Philippine diving.