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Zeno

Four years of
theory.
Zero days
of reality.

REAL CODEBASES

Code you didn’t write.

REAL ISSUES

Trace the bug. Ship the fix.

REAL REVIEWS

Feedback that feels real.

spendwise / auth.js
ANALYZING...
auth.js — token generation
const generateToken = (user) => {
const payload = { id: user._id };
const token = jwt.sign(payload, process.env.SECRET);
return token;
}
Awaiting analysis...
ISSUE: JWT_SECRET_EXPOSURE · DIFFICULTY: JUNIORPR PENDING
Problem

Most people learn coding in environments built around them.

But real systems don't care. The moment there's unfamiliar structure, hidden context, or too many moving parts... confidence disappears very quickly.

monorepo/
apps/
web/ (where is the entry point?)
api/
packages/
ui/
core-utils/
why is core-utils importing from web?!
docker-compose.yml
Makefile
Flow

You enter a realistic codebase. You get an issue. You try to understand what's happening. You make the fix. You get reviewed on your approach.

1. THE ISSUE

Duplicate order confirmation emails

"Hey, we've had 3 customers complain today that they received the 'Order Confirmed' email twice. It seems to only happen during traffic spikes."

2. THE CONTEXT
const processOrder = async (order) => {
await db.orders.save(order);
await emailService.sendConfirmation(order.id);
return { status: 'success' };
}
3. THE REVIEW

Senior Engineer

"Moving the email dispatch before the DB transaction commits means we might send an email for an order that fails to save. We need an outbox pattern here."
Common questions
01

Why not just contribute to open source directly?

You should — eventually. Jumping cold into a 100k-line codebase is how most people quit. Zeno builds the reps first.

02

Will the codebases actually feel realistic?

Real fragmented systems. Weird architecture. Hidden context. No toy apps, no counters.

01 — 05
03

Is this for beginners?

No. Post-tutorial, for developers who can build but can't yet navigate.

04

What kind of feedback do I get?

PR-style review — edge cases, architecture, implications. Not just pass/fail.

05

Do I need to set up anything locally?

No. Read, debug, and fix directly in the browser.

Most developers know how to build from scratch. Almost none are trained to navigate what already exists.

Before

Tutorial world

Controlled environments. You build what you define.

You are here

Zeno

Real codebases. Real bugs. Structured feedback on how you approached it.

Next

Open source

Real repos. Real teams. Real contribution.

Early feedback

This is still being built. If something resonates — or doesn't — I want to know before it ships.