Skill assessment & practice platform for the AI era

Even when AI writes the code, the responsibility is yours.

You can read the code. You know how it works. Only then can you look at AI's output and say it's good to ship. A browser-based programming practice platform for building that foundation, in the smallest form that works.

Start for free Browse problems

AI completion disabled
gVisor sandboxed execution
Real-time auto grading

app/api/todos/route.tsAI OFF

// POST /api/todos — implement to the specexport async function POST(req: Request) {  const body = await req.json();  const todo = todoSchema.parse(body);  const row = await db.insert(todos)    .values(todo).returning();  return Response.json(row, {    status: 201,  });}

$ kasane test --all

12/12 tests passed(1.24s)

Grading result

Frontend92
Backend88
Database76
Performance81

gVisor isolated runtime

18
Practice problems: 4
Evaluation layers: 8
Supported tech stacks: 100%
Browser-based

Supported stacks

Python
JavaScript / TypeScript
Go
Ruby
PHP
Java
C++
Rust
React / Next.js
Express
Hono
NestJS
FastAPI
Django
Rails
Laravel
Spring
PostgreSQL

Problem

The pitfall of the age when AI writes everything

AI will write the code for you. But if you can't read it, you can't judge whether it's right. Learners and educators alike get stuck here.

It runs, but you can't explain it

Hand it to AI and you get something that runs. But if you can't explain what's inside, you can't fix it, and you can't take responsibility for it.

Copy-paste builds no real skill

When pasting an answer is enough to pass, no hands-on experience accumulates. Learners feel they understand, but their skills never grow.

No yardstick for real skill

Looking at the finished product alone, you can't tell a person's ability from AI output. Educators and evaluators are left without anything to judge by.

Why write by hand

Write just the essentials, once, with your own hands.

You don't need to write everything from scratch. KASANE gives you three mechanisms to nail down just the parts that really matter, by hand.

ai.suggest(…)

OFF

AI completion off

Write with your own hands in an environment with code completion and generation turned off. For the time you spend on fundamentals, no leaning on AI.

Runs in a sandbox

Run what you write instantly in a gVisor-isolated environment. Run it, fix it, run it again. That loop is what stays with you.

Graded by layer

It doesn't stop at pass/fail. Full-stack problems are graded by layer — Frontend, Backend, Database, and Performance — so you see exactly which layers you can build.

Live Preview

The app you write runs right in your browser.

Write in the editor, save, and the preview next to it updates instantly. Next.js, your API, and the database all really run in your own dedicated environment. No dev-environment setup needed.

app/page.tsxPreview running

// Save, and the preview on the right updatesexport default function TodoApp() {  const { todos, addTodo } = useTodos();  return (    <main>      <h1>Today's tasks</h1>      <AddTodoForm onAdd={addTodo} />      <TodoList items={todos} />    </main>  );}

https://preview-3000.kasane.run

Today's tasks

Add a task...Add

Implement POST /api/todos
Make the tests pass
Check it in the previewjust now

$ npm run dev

Ready in 0.9s(port 3000)

Save to see it instantly

PostgreSQL in the same environment

Full stack, running as is

Frameworks like Next.js and Express boot with PostgreSQL in one click. Write with the same feel as local development.

Save it, see it

Fix the code and the preview updates instantly. Write while running and checking as you go.

Break it, no problem

A gVisor-isolated environment that's yours alone. Break it as many times as you like and rebuild in seconds.

4-Layer Evaluation

Don't stop at “it works” — evaluation layered four deep

KASANE takes its name from the Japanese tradition of layering colors (kasane). Full-stack problems are graded across four layers — Frontend, Backend, Database, and Performance — to reveal how far your code really goes.

Frontend

UI rendering and interaction tests

Backend

API spec compliance, error handling

Database

Data persistence and retrieval checks

Performance

Test execution time measurement

Overall rank is graded S / A / B / C

How it works

From sign-up to grading, everything runs in your browser

Sign up for free

Start with just an email address. No installation or environment setup required.

Pick a challenge

From basic algorithms to full-stack implementations, choose by level and goal.

Write and run in the browser

Editor, terminal, and DB client all live in your browser. Code runs instantly in an isolated sandbox.

Auto-graded with test cases

Submissions are graded instantly. Full-stack problems return results and feedback by layer: Frontend, Backend, Database, and Performance.

Package

What KASANE offers

React UI

REST API

PostgreSQL

Full-stack practice

Implement React, API, and DB end-to-end in a single problem

Automated grading engine

Real-time scoring through test-case-based automated evaluation

Layered evaluation

Full-stack problems evaluated by layer: Frontend, Backend, Database, and Performance

$ run tests

POST /todos · 201

type-check passed

△ N+1 query detected

Real-time feedback

Instant feedback on test results, lint, and type checks

browser IDE

Browser-based IDE

No setup required. A full-featured editor based on Monaco Editor

Skill visualization

Visualize skill growth with radar charts and heatmaps

Use Cases

Used across a wide range of settings

Coding schools & bootcamps

Visualize learners' skills with real-world-like problems. Objectively prove their ability at graduation.

Corporate engineer training

Accurately gauge the practical ability of new and mid-career engineers. Measure training effectiveness and provide individual follow-up.

Universities & educational institutions

As an automated grading foundation for programming courses. Reduce instructor workload and evaluate students' skills accurately.

Founder's Message

Why I built KASANE

With AI agents, people can ship apps even without prior knowledge. Many already are. The times have changed.

Still, taking responsibility for the resulting code is a separate matter. Even when AI wrote it, you are the one shipping it. You can read code. You understand how things and the architecture work. Only then can you say "this part is solid" or "this should be fixed." Even instructing the AI well requires that foundation.

KASANE is a place to build that foundation — the minimum needed, no more. What is an API? How is it actually implemented? Write the basics once, by hand. Run it instantly in the browser, fix it instantly. You do not need to write everything from scratch. Pinning down only the parts that really matter, with your own hands, is enough.

I hope you take the eye you sharpen here, put AI to work, and keep accelerating the world's IT. I am here to support that.

Support

Support tailored to your needs

Curriculum design

Training materials

Progress dashboard

Technical mentoring

Report creation

Custom problem creation

API integration

Onboarding support

Have questions? Feel free to reach out

From adoption consultations to curriculum design and custom problem creation — start by getting in touch.

For You

Find the way that fits you

For individuals

As the next step after learning the basics. Tackle real-world problems and build skills valued in the job market.

Learn more

For businesses

Close the practical gap after training. Objectively visualize engineers' skills and improve development efficiency.

See business plans

For educational institutions

As a grading foundation for programming courses. Automated grading reduces instructor workload and evaluates students accurately.

See plans for education

FAQ

Frequently asked questions

What skill levels is KASANE suited for?

It supports a wide range, from those who have learned programming basics (variables, functions, conditionals, etc.) to experienced engineers. Problems are organized by difficulty, from basic CRUD implementation to advanced themes like N+1 query optimization and transaction design.

Is environment setup required?

No, none at all. KASANE is a fully browser-based platform. A Monaco-Editor-based code editor, terminal, and database client all run in the browser. You can start coding right after signing up.

How does automated grading work?

It uses a test-case-based automated grading engine. Lessons and algorithm problems are judged by input/output matching. Full-stack problems are graded by layer — Frontend (UI display/operation), Backend (API spec compliance), and Database (data persistence) — with Performance measured as test execution time. Results are scored with S/A/B/C ranks.

What support is available when adopting it for corporate training?

We provide total support from planning to outcome measurement — curriculum design consulting, custom problem creation, a learner progress dashboard, and skill reports. Feel free to get in touch.

What tech stacks are supported?

We support 8 languages: Python, Go, Java, C++, Rust, JavaScript/TypeScript, Ruby, and PHP. Full-stack challenges run on React (Next.js) for the frontend and up to 10 backend frameworks — Node.js (Express/Hono/NestJS), Python (FastAPI/Django), Go, Ruby (Rails), PHP (Laravel), and Java (Spring) — with PostgreSQL for the database. You can solve the same challenge in your preferred stack, and we plan to expand coverage over time.

What is the pricing?

Individual use can be tried from a free plan. Business and education plans are tailored to the number of users and customization needs. Please contact us for details.

Start building practical skills now

Sign-up is free. No setup required — start coding from your browser right now.

Even when AI writes the code, the responsibility is yours.

AI completion disabled

gVisor sandboxed execution

Real-time auto grading

// POST /api/todos — implement to the specexport async function POST(req: Request) { const body = await req.json(); const todo = todoSchema.parse(body); const row = await db.insert(todos) .values(todo).returning(); return Response.json(row, { status: 201, });}

// Save, and the preview on the right updatesexport default function TodoApp() { const { todos, addTodo } = useTodos(); return ( <main> <h1>Today's tasks</h1> <AddTodoForm onAdd={addTodo} /> <TodoList items={todos} /> </main> );}