ElCampeon Apps

Learning apps, built with Claude

Android apps for people learning security and computer science, free to download with no account needed. Written with Claude Code, and getting tutors that run on the Claude API.

All apps on Google Play How the AI will work

SecurityLearn Web Application SecurityLive
Computer scienceLearn Algorithms & DSLive
HealthBMI CalculatorLive

On Google Play now

Three apps. No account needed.

All three are free to download. The two learning apps show ads and offer an optional Pro upgrade; BMI Calculator is completely free with no ads. Each one is getting a Claude feature. The phones below show the idea; the features are in development and aren't in the apps yet.

Live on Google PlayFree downloadAds · optional ProNo account

Learn Web Application Security

An introduction to the most common web vulnerabilities: how they're exploited, and how they're fixed.

Planned Claude feature: security tutorIn development

Explains any vulnerability in plain language, then generates practice questions for your level.

Get it on Google Play

Security tutorClaude · in development

Why is changing the invoice ID in the URL a vulnerability?

The server checks you're signed in, but not that the invoice is yours. That's broken object-level authorization: BOLA.

Quick check. Which fix stops it?A. Hide the ID in the pageB. Look it up by ID and owner

Right. Hiding the ID doesn't help: an attacker never needed your page.

Ask about any vulnerability…

Illustrative example. Feature in development.

Live on Google PlayFree downloadAds · optional ProNo account

Learn Algorithms & DS

Core algorithms and data structures, explained step by step.

Planned Claude feature: algorithm tutorIn development

Walks through an algorithm using your own example input, one step at a time.

Get it on Google Play

Algorithm tutorClaude · in development

Binary search for 23 in [4, 9, 15, 23, 42]

Step 1: low 0, high 4, mid 2 → 15. 23 is bigger, so keep the right half.

Step 2: low 3, high 4, mid 3 → 23. Found at index 3 in two steps.

Why not just check every item?

That's linear search: up to 5 checks here. Halving the range each step takes about log₂ n.

Give me an input to trace…

Illustrative example. Feature in development.

Live on Google PlayFree, no adsNo account

BMI Calculator

Calculate your body mass index and see which standard range it falls in. Your numbers stay on your device.

Planned Claude feature: general guidanceIn development

General diet and activity suggestions for your BMI range, clearly marked as not medical advice.

Get it on Google Play

BMI guidanceClaude · in development

My BMI is 27.4. What does that mean?

27.4 is in the standard "overweight" range, 25 to 29.9. BMI is a rough screening number; it doesn't measure body fat.

General ideas: walk most days, add vegetables and fibre, cut back on sugary drinks.

This isn't medical advice. A doctor can tell you what's right for you.

Ask about your range…

Illustrative example. Feature in development.

How the AI features will work

Your phone never holds a key

Requests go through a small server we control, so we can protect the key and limit abuse. In development

Your phone

The app sends only the question you type. No account, no device identifiers, and no API key.

Our Cloudflare Worker

Holds the key, applies rate limits, and keeps no logs of your questions.

Claude API

Anthropic's model writes the answer, which comes straight back to the app.

Attacked before it ships

We test our own AI features for prompt injection and data leaks before release. It's the same testing we do for clients.

General, not medical

Health guidance stays general, and tells people to see a doctor for anything specific to them.

Privacy first

Our privacy policy will be updated to describe exactly what is sent before any AI feature is released.

Feedback

Tell us what to add or fix.

[email protected]

Feedback on our apps

Every message gets read. We reply within two working days.

Found a flaw in our apps?

Report it to the same address. See our disclosure policy.