freeCodeCamp Curriculum & Platform Development

Skill by ara.so — Daily 2026 Skills collection.

freeCodeCamp.org is a free, open-source learning platform with thousands of interactive coding challenges, certifications, and a full-stack curriculum. The codebase includes a React/TypeScript frontend, Node.js/Fastify backend, and a YAML/Markdown-based curriculum system.

Architecture Overview

freeCodeCamp/
├── api/                   # Fastify API server (TypeScript)
├── client/                # Gatsby/React frontend (TypeScript)
├── curriculum/            # All challenges and certifications (YAML/Markdown)
│   └── challenges/
│       ├── english/
│       │   ├── responsive-web-design/
│       │   ├── javascript-algorithms-and-data-structures/
│       │   └── ...
│       └── ...
├── tools/
│   ├── challenge-helper-scripts/  # CLI tools for curriculum authoring
│   └── ui-components/             # Shared React components
├── config/                # Shared configuration
└── e2e/                   # Playwright end-to-end tests

Local Development Setup

Prerequisites

• Node.js 20+ (use nvm or fnm)
• pnpm 9+
• MongoDB (local or Atlas)
• A GitHub account (for OAuth)

1. Fork & Clone

git clone https://github.com/<YOUR_USERNAME>/freeCodeCamp.git
cd freeCodeCamp

2. Install Dependencies

pnpm install

3. Configure Environment

cp sample.env .env

Key .env variables to set:

# MongoDB
MONGOHQ_URL=mongodb://127.0.0.1:27017/freecodecamp

# GitHub OAuth (create at github.com/settings/developers)
GITHUB_ID=$GITHUB_OAUTH_CLIENT_ID
GITHUB_SECRET=$GITHUB_OAUTH_CLIENT_SECRET

# Auth
JWT_SECRET=$YOUR_JWT_SECRET
SESSION_SECRET=$YOUR_SESSION_SECRET

# Email (optional for local dev)
SENDGRID_API_KEY=$SENDGRID_API_KEY

4. Seed the Database

pnpm run seed

5. Start Development Servers

# Start everything (API + Client)
pnpm run develop

# Or start individually:
pnpm run develop:api      # Fastify API on :3000
pnpm run develop:client   # Gatsby on :8000

Curriculum Challenge Structure

Challenges are stored as YAML/Markdown files under curriculum/challenges/.

Challenge File Format

# curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/comment-your-javascript-code.md

---
id: bd7123c8c441eddfaeb5bdef  # unique MongoDB ObjectId-style string
title: Comment Your JavaScript Code
challengeType: 1              # 1=JS, 0=HTML, 2=JSX, 3=Vanilla JS, 5=Project, 7=Video
forumTopicId: 16783
dashedName: comment-your-javascript-code
---

# --description--

Comments are lines of code that JavaScript will intentionally ignore.

```js
// This is an in-line comment.
/* This is a multi-line comment */

--instructions--

Try creating one of each type of comment.

--hints--

hint 1

assert(code.match(/(\/\/)/).length > 0);

hint 2

assert(code.match(/(\/\*[\s\S]+?\*\/)/).length > 0);

--seed--

--seed-contents--

// Your starting code here

--solutions--

// inline comment
/* multi-line
   comment */

### Challenge Types

| Type | Value | Description |
|------|-------|-------------|
| HTML | 0 | HTML/CSS challenges |
| JavaScript | 1 | JS algorithm challenges |
| JSX | 2 | React component challenges |
| Vanilla JS | 3 | DOM manipulation |
| Python | 7 | Python challenges |
| Project | 5 | Certification projects |
| Video | 11 | Video-based lessons |

---

## Creating a New Challenge

### Using the Helper Script

```bash
# Create a new challenge interactively
pnpm run create-challenge

# Or use the helper directly
cd tools/challenge-helper-scripts
pnpm run create-challenge --superblock responsive-web-design --block css-flexbox

Manual Creation

1. Find the correct directory under curriculum/challenges/english/
2. Create a new .md file with a unique ID

# Generate a unique challenge ID
node -e "const {ObjectID} = require('mongodb'); console.log(new ObjectID().toString())"

3. Follow the challenge file format above

Validate Your Challenge

# Lint and validate all curriculum files
pnpm run test:curriculum

# Test a specific challenge
pnpm run test:curriculum -- --challenge <challenge-id>

# Test a specific block
pnpm run test:curriculum -- --block basic-javascript

Writing Challenge Tests

Tests use a custom assertion library. Inside # --hints-- blocks:

JavaScript Challenges

# --hints--

`myVariable` should be declared with `let`.

```js
assert.match(code, /let\s+myVariable/);

The function should return true when passed 42.

assert.strictEqual(myFunction(42), true);

The DOM should contain an element with id main.

const el = document.getElementById('main');
assert.exists(el);

### Available Test Utilities

```js
// DOM access (for HTML challenges)
document.querySelector('#my-id')
document.getElementById('test')

// Code inspection
assert.match(code, /regex/);          // raw source code string
assert.include(code, 'someString');

// Value assertions (Chai-style)
assert.strictEqual(actual, expected);
assert.isTrue(value);
assert.exists(value);
assert.approximately(actual, expected, delta);

// For async challenges
// Use __helpers object
const result = await fetch('/api/test');
assert.strictEqual(result.status, 200);

API Development (Fastify)

Route Structure

// api/src/routes/example.ts
import { type FastifyPluginCallbackTypebox } from '../helpers/plugin-callback-typebox';
import { Type } from '@fastify/type-provider-typebox';

export const exampleRoutes: FastifyPluginCallbackTypebox = (
  fastify,
  _options,
  done
) => {
  fastify.get(
    '/example/:id',
    {
      schema: {
        params: Type.Object({
          id: Type.String()
        }),
        response: {
          200: Type.Object({
            data: Type.String()
          })
        }
      }
    },
    async (req, reply) => {
      const { id } = req.params;
      return reply.send({ data: `Result for ${id}` });
    }
  );

  done();
};

Adding a New API Route

// api/src/app.ts - register the plugin
import { exampleRoutes } from './routes/example';

await fastify.register(exampleRoutes, { prefix: '/api' });

Database Access (Mongoose)

// api/src/schemas/user.ts
import mongoose from 'mongoose';

const userSchema = new mongoose.Schema({
  email: { type: String, required: true, unique: true },
  completedChallenges: [
    {
      id: String,
      completedDate: Number,
      solution: String
    }
  ]
});

export const User = mongoose.model('User', userSchema);

Client (Gatsby/React) Development

Adding a New Page

// client/src/pages/my-new-page.tsx
import React from 'react';
import { Helmet } from 'react-helmet';
import { useTranslation } from 'react-i18next';

const MyNewPage = (): JSX.Element => {
  const { t } = useTranslation();

  return (
    <>
      <Helmet>
        <title>{t('page-title.my-new-page')} | freeCodeCamp.org</title>
      </Helmet>
      <main>
        <h1>{t('headings.my-new-page')}</h1>
      </main>
    </>
  );
};

export default MyNewPage;

Using the Redux Store

// client/src/redux/selectors.ts pattern
import { createSelector } from 'reselect';
import { RootState } from './types';

export const userSelector = (state: RootState) => state.app.user;

export const completedChallengesSelector = createSelector(
  userSelector,
  user => user?.completedChallenges ?? []
);

// In a component
import { useAppSelector } from '../redux/hooks';
import { completedChallengesSelector } from '../redux/selectors';

const MyComponent = () => {
  const completedChallenges = useAppSelector(completedChallengesSelector);
  return <div>{completedChallenges.length} challenges completed</div>;
};

i18n Translations

// Add keys to client/i18n/locales/english/translations.json
{
  "my-component": {
    "title": "My Title",
    "description": "My description with {{variable}}"
  }
}

// Use in component
const { t } = useTranslation();
t('my-component.title');
t('my-component.description', { variable: 'value' });

Testing

Unit Tests (Jest)

# Run all unit tests
pnpm test

# Run tests for a specific package
pnpm --filter api test
pnpm --filter client test

# Watch mode
pnpm --filter client test -- --watch

Curriculum Tests

# Validate all challenges
pnpm run test:curriculum

# Validate specific superblock
pnpm run test:curriculum -- --superblock javascript-algorithms-and-data-structures

# Lint challenge markdown
pnpm run lint:curriculum

E2E Tests (Playwright)

# Run all e2e tests
pnpm run test:e2e

# Run specific test file
pnpm run test:e2e -- e2e/learn.spec.ts

# Run with UI
pnpm run test:e2e -- --ui

Writing E2E Tests

// e2e/my-feature.spec.ts
import { test, expect } from '@playwright/test';

test('user can complete a challenge', async ({ page }) => {
  await page.goto('/learn/javascript-algorithms-and-data-structures/basic-javascript/comment-your-javascript-code');

  // Fill in the code editor
  await page.locator('.monaco-editor').click();
  await page.keyboard.type('// inline comment\n/* block comment */');

  // Run tests
  await page.getByRole('button', { name: /run the tests/i }).click();

  // Check results
  await expect(page.getByText('Tests Passed')).toBeVisible();
});

Key pnpm Scripts Reference

# Development
pnpm run develop              # Start all services
pnpm run develop:api          # API only
pnpm run develop:client       # Client only

# Building
pnpm run build                # Build everything
pnpm run build:api            # Build API
pnpm run build:client         # Build client (Gatsby)

# Testing
pnpm test                     # Unit tests
pnpm run test:curriculum      # Validate curriculum
pnpm run test:e2e             # Playwright e2e

# Linting
pnpm run lint                 # ESLint all packages
pnpm run lint:curriculum      # Curriculum markdown lint

# Database
pnpm run seed                 # Seed DB with curriculum data
pnpm run seed:certified-user  # Seed a test certified user

# Utilities
pnpm run create-challenge     # Interactive challenge creator
pnpm run clean                # Clean build artifacts

Superblock & Block Naming Conventions

Superblocks map to certifications. Directory names use kebab-case:

responsive-web-design/
javascript-algorithms-and-data-structures/
front-end-development-libraries/
data-visualization/
relational-database/
back-end-development-and-apis/
quality-assurance/
scientific-computing-with-python/
data-analysis-with-python/
machine-learning-with-python/
coding-interview-prep/
the-odin-project/
project-euler/

Block directories within a superblock:

responsive-web-design/
├── basic-html-and-html5/
├── basic-css/
├── applied-visual-design/
├── css-flexbox/
└── css-grid/

Common Patterns & Gotchas

Challenge ID Generation

Every challenge needs a unique 24-character hex ID:

// tools/challenge-helper-scripts/helpers/id-gen.ts
import { ObjectId } from 'bson';
export const generateId = (): string => new ObjectId().toHexString();

Adding Forum Links

Every challenge needs a forumTopicId linking to forum.freecodecamp.org:

forumTopicId: 301090  # Must be a real forum post ID

Curriculum Meta Files

Each block needs a _meta.json:

{
  "name": "Basic JavaScript",
  "dashedName": "basic-javascript",
  "order": 0,
  "time": "5 hours",
  "template": "",
  "required": [],
  "isUpcomingChange": false,
  "isBeta": false,
  "isLocked": false,
  "isPrivate": false
}

Testing with Authentication

// In e2e tests, use the test user fixture
import { authedUser } from './fixtures/authed-user';

test.use({ storageState: 'playwright/.auth/user.json' });

test('authenticated action', async ({ page }) => {
  // page is already logged in
  await page.goto('/settings');
  await expect(page.getByText('Account Settings')).toBeVisible();
});

Troubleshooting

MongoDB Connection Issues

# Check if MongoDB is running
mongosh --eval "db.adminCommand('ping')"

# Start MongoDB (macOS with Homebrew)
brew services start mongodb-community

# Use in-memory MongoDB for tests
MONGOHQ_URL=mongodb://127.0.0.1:27017/freecodecamp-test pnpm test

Port Conflicts

# API runs on 3000, Client on 8000
lsof -i :3000
kill -9 <PID>

Curriculum Validation Failures

# See detailed error output
pnpm run test:curriculum -- --verbose

# Common issues:
# - Missing forumTopicId
# - Duplicate challenge IDs
# - Invalid challengeType
# - Malformed YAML frontmatter

Node/pnpm Version Mismatch

# Use the project's required versions
node --version   # Should match .nvmrc
pnpm --version   # Should match packageManager in package.json

nvm use          # Switches to correct Node version

Client Build Errors

# Clear Gatsby cache
pnpm --filter client run clean
pnpm run develop:client

Contributing Workflow

# 1. Create a feature branch
git checkout -b fix/challenge-typo-in-basic-js

# 2. Make changes and test
pnpm run test:curriculum
pnpm test

# 3. Lint
pnpm run lint

# 4. Commit using conventional commits
git commit -m "fix(curriculum): correct typo in basic-javascript challenge"

# 5. Push and open PR against main
git push origin fix/challenge-typo-in-basic-js

Commit message prefixes: fix:, feat:, chore:, docs:, refactor:, test:

Resources

• Contribution guide: https://contribute.freecodecamp.org
• Forum: https://forum.freecodecamp.org
• Discord: https://discord.gg/PRyKn3Vbay
• How to report bugs: https://forum.freecodecamp.org/t/how-to-report-a-bug/19543