Coding project ideas: 18 projects by level, each with a first version and a stretch goal

01 Bill splitter with uneven shares

A form that splits a restaurant bill between people who ate different amounts, with tax and tip shared in proportion.

Stack

Any language; one web page or a command line.

Teaches

Functions, input validation, money as integer cents, rounding.

First version

Names and item prices in, each person’s total out.

Stretch goal

Shares add up to the bill to the cent, and past bills are saved.

Time

3 to 6 hours.

The trap is rounding. Three people splitting USD 100.00 evenly get 33.33 each, and the three amounts add up to 99.99. Decide where the missing cent goes, write the rule down and test it. Store money as whole cents, never as decimals, so 33.33 is 3333. The same habit protects every payment system you will ever touch.

Write a function split_bill(items, tax_cents, tip_cents) where items is a list of (person, price_cents). Tax and tip are shared in proportion to what each person ordered. Return a dict of person to total cents. The totals must add up to exactly the bill: give leftover cents to the people with the largest remainders. Do not build a user interface yet.
Tests to pass: two people with items 1000 and 3000 and tax 400 give 1100 and 3300. Three people sharing one item of 10000 cents give 3334, 3333 and 3333.

02 Habit streak tracker

A page or script where you tick off habits each day and see the current streak and the longest streak.

Stack

HTML and JavaScript with browser storage, or Python with a JSON file.

Teaches

Dates, persistence, one pure function for the streak logic.

First version

A list of habits, a tick for today, a current streak computed from ticked dates.

Stretch goal

Allow skip days (for example five of seven) and draw a 12-week grid.

Time

4 to 8 hours.

Streak logic breaks at midnight, at month ends and when someone forgets for a day. Write streak(ticked_dates, today) as a function with no screen code in it, and test it: ticks on yesterday and today give 2; a tick on yesterday only gives 1, because the streak is alive until today ends; a last tick two days ago gives 0.

03 Recipe scaler

Paste a recipe, say how many servings you want, and get every quantity rescaled in fractions you can measure.

Stack

Python or JavaScript; plain text in, plain text out.

Teaches

String parsing, fractions, units, deciding what to do with edge cases.

First version

Lines like “1 1/2 cups flour” are multiplied by a factor and printed as tidy fractions.

Stretch goal

Convert cups to grams for ten ingredients you list yourself.

Time

6 to 10 hours.

Python’s fractions module does exact arithmetic, so 1 1/2 times 2/3 is exactly 1. In JavaScript you write a small greatest-common-divisor function yourself, which is a good exercise. The interesting part is the rules: 2 eggs scaled by 1.5 is 3, but 1 egg scaled by 1.5 is 1.5. Do you round to the nearest half? Your answer is the project.

04 Time zone meeting planner

Pick two to four cities and see which hours work for all of them, with daylight saving time handled correctly.

Stack

JavaScript with the built-in Intl API, or Python with zoneinfo.

Teaches

Dates and time zones, why you never do the arithmetic by hand, lookup tables.

First version

A 24-hour grid for the first city, the matching local times for the others, and the hours that fall between 9:00 and 18:00 everywhere highlighted.

Stretch goal

A shareable link that stores the cities and the date in the URL.

Time

6 to 10 hours.

Use a library or built-in that reads the IANA time zone database. Then test with dates where clocks change. In 2027 the United States moves its clocks on March 14 and most of Europe on March 28, so for two weeks New York is 4 hours behind London instead of 5. If your grid shows 5 hours on March 20, 2027, it is wrong.

05 Dice scorer for a Yahtzee-style game

Given five dice, return every scoring category and its points: pairs, full house, straights and the five-of-a-kind.

Stack

Any language; command line.

Teaches

Loops, counting with dictionaries, unit tests, pure functions.

First version

score(dice) returns a mapping of category to points under the rules you write down.

Stretch goal

A computer player that picks the best category each turn; compare it with random play over 10,000 games.

Time

4 to 8 hours.

This is the best project for learning tests, because the right answers are easy to write by hand. Under the standard rules a full house scores 25, a small straight 30, a large straight 40 and a five-of-a-kind 50. Write twenty examples first: [2,2,3,3,3] is a full house, [1,2,3,4,5] is a large straight, [4,4,4,4,4] is a five-of-a-kind and also a full house in some rule sets. Pick a rule and keep it.

06 Personal links page, deployed

A one-page site with your name, a short bio and five links, live on a public URL that you did not have to pay for.

Stack

HTML and CSS, git, a free static host such as GitHub Pages or Cloudflare Pages.

Teaches

HTML structure, CSS layout, responsive design, git, deployment.

First version

One index.html that reads well on a phone and is live.

Stretch goal

Dark mode with prefers-color-scheme, a custom domain, and the issues that Lighthouse in Chrome DevTools flags fixed.

Time

3 to 6 hours.

Do this one early. Most beginner projects die on the laptop where they were built, and deploying once removes the mystery. The MDN learning area covers the HTML and CSS you need. Put the project in git on day one and commit each time something works.

01 URL shortener with click counts

A service that turns a long link into a short code, redirects visitors and counts the clicks.

Stack

Node with Express, or Python with Flask or FastAPI; SQLite or Postgres.

Teaches

HTTP redirects, routing, schema design, unique constraints, input validation.

First version

POST a URL and get a code; GET /code redirects and adds one to a counter.

Stretch goal

Custom aliases, expiry dates, a stats page with clicks per day, and a block on redirect loops.

Time

12 to 20 hours.

Generate codes from seven random letters and digits: that is 62 to the power of 7, about 3.5 trillion combinations. Put a unique index on the code and retry when an insert collides, instead of checking first. Redirect with a 302, not a 301: browsers may cache a 301 and skip your server, which stops the click count. Accept only http and https links, or someone will shorten a javascript: URL.

Build a URL shortener with FastAPI and SQLite. POST /links with a JSON body {url} returns {code}. GET /{code} responds 302 to the stored URL and increments clicks. Rules: only http and https URLs are accepted (400 otherwise); codes are 7 random characters from a-z, A-Z, 0-9; the code column has a unique index and the insert retries on conflict; unknown codes return 404.
Do not build: accounts, a front end, analytics beyond one counter.
Write pytest tests for each rule, including a javascript: URL and a forced code collision.

02 Real-time chat room with presence

A single chat room where messages appear instantly for everyone and a list shows who is online.

Stack

Node or Python on the server, plain JavaScript in the page, the WebSocket API.

Teaches

Persistent connections, broadcasting, reconnection, shared state across clients.

First version

One room, a nickname, messages sent to every connected client, an online list.

Stretch goal

Several rooms, the last 50 messages on join, reconnect with backoff, a rate limit per connection.

Time

15 to 25 hours.

The bug everyone meets is a dead connection that never sends a close event, such as a laptop lid shut on a train. The user stays online forever. The fix is a heartbeat: send a ping every 30 seconds and drop any connection that misses two in a row. Test it by killing the client process rather than closing the tab.

03 Job application tracker with reminders

A private board where you log each application, move it through statuses and get a reminder when nothing has happened for a week.

Stack

A full-stack framework (Next.js, Django, Rails or Laravel), Postgres, an email service.

Teaches

Sign-in, CRUD, per-user data, scheduled jobs, sending email.

First version

Sign up, add an application (company, role, status, date), change its status, filter by status.

Stretch goal

A reminder seven days after “applied” with no update, CSV import, an .ics export for interviews.

Time

25 to 40 hours.

A related idea, JobsFlow, is posted on the board and goes further: tailoring the resume and drafting follow-ups. The test that matters here is plain. User A must not be able to read user B’s application by changing the ID in the URL. Write that test before you build the second screen. OWASP lists broken access control among the most common web risks, and this is the simplest form of it.

Read “Job application tracker with reminders” on the board and copy its build prompt →

04 Booking page for one person

A public page where visitors pick a free slot from your availability, and both of you get a confirmation.

Stack

A full-stack framework, Postgres, an email service, an .ics attachment.

Teaches

Time zones, availability rules, transactions, unique constraints, race conditions.

First version

Availability of Monday to Friday, 9:00 to 17:00, 30-minute slots; booking stores a name and email; a taken slot disappears.

Stretch goal

Buffers between meetings, blocked holidays, a cancel link, Google Calendar sync.

Time

25 to 40 hours.

Two visitors will click the same slot within a second. Put a unique index on the slot start time and let the database refuse the second insert, then show that visitor a message such as “that slot was just taken” instead of an error page. Store every time in UTC and convert only when you display it.

Build a booking page for one host. Tables: bookings(id, slot_start_utc unique, name, email, created_at). Availability is Monday to Friday 09:00 to 17:00 in the host’s time zone, in 30-minute slots, shown to the visitor in their own time zone.
Rules: a slot already in bookings is not offered; if two requests book the same slot, the second gets a 409 and a friendly message; no slot in the past.
Do not build: accounts, payments, calendar sync, cancellation.
Write a test that fires two bookings for the same slot at once and expects exactly one success.

05 Static blog generator from Markdown

A command that reads a folder of Markdown files and writes a complete website with an index page and an RSS feed.

Stack

Node or Python, a Markdown library, a template engine such as Jinja.

Teaches

File input and output, front matter parsing, templates, command line design, build pipelines.

First version

Each .md file with a title and date at the top becomes an HTML page; the index lists them newest first.

Stretch goal

Tag pages, syntax highlighting, rebuild only changed files, a dev server with live reload.

Time

15 to 25 hours.

Keep three things apart: content (the Markdown), layout (the templates) and output (the generated folder, which you never edit by hand). Add a link checker as the last step of the build. A generator that publishes broken links between its own pages has failed at the one thing it was for.

06 Webhook receiver that processes each event once

A small service that accepts payment events from a provider’s test mode, checks the signature and stores each event exactly once.

Stack

Any HTTP framework, SQLite or Postgres, a payment provider’s test mode.

Teaches

HMAC signatures, idempotency, retries, reading the raw request body.

First version

An endpoint that verifies the signature, inserts the event ID under a unique constraint and answers 200 quickly.

Stretch goal

A replay command, a dead-letter table for events whose handler failed, a small dashboard.

Time

10 to 20 hours.

Providers retry deliveries, so the same event will arrive more than once. A unique constraint on the event ID makes the second delivery harmless. The classic failure is a JSON middleware that parses the body before you verify the signature: the bytes change and every check fails. Stripe’s webhook documentation shows the pattern, and the same idea applies to any provider that signs its requests.

01 Offline-first notes app with sync

A notes app that works without a connection, then syncs to a server and resolves edits made on two devices.

Stack

A browser app with IndexedDB and a service worker, plus a small server API.

Teaches

Local-first design, sync protocols, conflict resolution, versioning.

First version

Notes saved locally and usable offline; on reconnect, changes are pushed and the newest edit wins.

Stretch goal

Merge text changes instead of overwriting, show real conflicts to the user, encrypt notes before they leave the device.

Time

40 to 70 hours.

Device clocks are wrong often enough to matter, so do not decide “newest” by a timestamp from the client. Have the server hand out a version number per note and reject an update that is based on an old one. Then write the test that proves it: two clients edit the same note offline, both reconnect, and nothing is silently lost.

02 Background job queue with retries and a dashboard

A queue built on a database table, with workers that claim jobs safely, retry failures with backoff and report their state.

Stack

Postgres, a worker in any language, a small web dashboard.

Teaches

Concurrency, row locking, retries with exponential backoff, idempotency, dead letters, metrics.

First version

A jobs table with status, run_at and attempts; a worker claims one job and marks it done or failed.

Stretch goal

Several workers at once, per-job timeouts, a dead-letter list, charts of queue depth and age of the oldest job.

Time

30 to 50 hours.

The core trick is that two workers must never take the same job. Postgres supports this with a locking clause, FOR UPDATE SKIP LOCKED, described in the SELECT documentation. A failed job gets run_at set to now plus 2 to the power of attempts seconds, so retries slow down instead of hammering a broken service. Test with ten workers and a thousand jobs, and count that each job ran once.

Build a job queue on Postgres. Table jobs(id, payload jsonb, status, run_at, attempts, last_error). A worker loop claims one due job with SELECT ... FOR UPDATE SKIP LOCKED, runs a handler, and sets status to done; on error it increments attempts and sets run_at to now + 2^attempts seconds; after 5 attempts status becomes dead.
Do not build: a dashboard, priorities, scheduling by cron.
Test: enqueue 1000 jobs, start 10 workers, assert every job ran exactly once and the total handler calls equal 1000.

03 Query engine over CSV files

A tiny SQL-like engine that runs statements such as SELECT name FROM people WHERE age > 30 LIMIT 10 against CSV files.

Stack

Any language with good string handling: Python, Go, Rust or TypeScript.

Teaches

Tokenizing, parsing into a tree, evaluating, query plans, streaming rows.

First version

A tokenizer, a parser for SELECT, WHERE and LIMIT, and an evaluator that streams rows.

Stretch goal

ORDER BY, GROUP BY with COUNT and SUM, a join on one key, an EXPLAIN command that prints the plan.

Time

40 to 80 hours.

You have a free test oracle: load the same CSV into SQLite, run the same 50 queries in both and compare the results. Every difference is a bug in your engine or a decision you should write down. Parse into a tree before you evaluate. Engines that evaluate while parsing cannot support GROUP BY later.

04 Multi-tenant app skeleton with billing

The parts every paid product needs and tutorials skip: organizations, roles, permissions and a plan that limits what an organization can do.

Stack

A full-stack framework, Postgres with row-level security or strict query scoping, a payment provider’s test mode.

Teaches

Tenancy modeling, authorization, billing state, webhooks, migrations.

First version

Organizations with owner and member roles, every query scoped by organization ID, a plan field set by a webhook event.

Stretch goal

Invites, an audit log, seat limits, a downgrade that keeps data, automated cross-tenant tests.

Time

60 to 100 hours.

Run it in the provider’s test mode only. The work is in the tests: for every route, log in as a member of organization A and request organization B’s data, and assert a 404 or 403. Generate those tests from your route list so a new route cannot ship without one.

05 Content-addressed version store

A command line tool that saves snapshots of a folder by the hash of their contents, lists history and restores any version.

Stack

Go, Rust, Python or Node; SHA-256 from the standard library; plain files on disk.

Teaches

Hashing, content-addressed storage, trees, deduplication, diffing.

First version

save writes each file into an objects folder named by its hash; log lists snapshots; restore writes one back.

Stretch goal

Identical files stored once across versions, a diff between two snapshots, cleanup of unreachable objects.

Time

30 to 60 hours.

Git itself works this way, and the Git Internals chapter of the Pro Git book walks through the object model. A related idea is posted on the board: version history for people who will never use git. A friendly interface on top of this store would answer it.

Read “Content-addressed version store” on the board and copy its build prompt →

06 Mini CI runner

A service that watches a repository, runs a command on every new commit and shows a pass or fail page.

Stack

Any backend language, subprocess handling, a git binary; Docker optional.

Teaches

Process management, timeouts, isolation, queues, streaming logs.

First version

Every 60 seconds run git fetch; on a new commit run ./test.sh with a 5-minute timeout and store the exit code and output.

Stretch goal

GitHub webhooks instead of polling, runs inside a container with CPU and memory limits, a status badge, parallel jobs.

Time

30 to 50 hours.