Codecell: Python & JS Tracer
See every line your code runs
Free · In‑App Purchases · Designed for iPad. Not verified for macOS.
Python and JavaScript in one library. Replay any run line by line with every variable, set breakpoints, use the REPL, and run scripts from Shortcuts — all on the device.
Most code apps stop at "press run, read the output". Codecell starts there and then shows you what your program actually did, one line at a time.
ONE LIBRARY, TWO LANGUAGES
A script is Python or JavaScript, and both sit in the same library. The same tracer, the same variables inspector, the same REPL and the same assistant work on either one. There is no mode to switch and no second app to buy.
REPLAY ANY RUN, WITH BREAKPOINTS
Press Trace instead of Run and Codecell records the program as it executes: every line, every call and return, and the value of every variable at each step. Scrub back and forth, play it like a video, and watch a loop go wrong at the exact moment it does. Tap a line number to set a breakpoint; playback runs to it and stops, and Continue jumps to the next one. This is the pen-and-paper trace a teacher draws on a whiteboard, done by the interpreter itself.
SEE THE VARIABLES
After any run, the Variables tab lists every name your program defined, with its type and value — dicts, lists, objects, functions and classes included. No print statements, no console.log.
A REPL THAT REMEMBERS
Open the REPL from your script library and an interactive session stays alive between entries: define something, use it in the next one, restart when you want a clean slate. Expressions show their value; history is one tap away.
AN ASSISTANT THAT RUNS YOUR CODE
On iPhones with Apple Intelligence, the assistant reads the script you are looking at, runs it to see the real output or error, explains what went wrong, and offers a corrected version. Every suggestion is checked for syntax errors before you see it, and nothing is applied until you tap Apply. It uses Apple's on-device model — no account, no API key, and nothing you write leaves the phone.
RUN FROM SHORTCUTS
Every saved script is a "Run Script" action in the Shortcuts app. Transform text, compute a value, or process the output of another action — offline, with no server.
IT ALL WORKS ON A PLANE
CPython 3.14 is built into the app and JavaScript runs on the engine iOS already ships. Neither calls out to anything. The Python standard library comes along: json, sqlite3, re, datetime, hashlib, math, itertools, zlib and the rest.
AN EDITOR MADE FOR A PHONE
Syntax highlighting from the same tree-sitter grammars your desktop editor uses. Errors marked as you type, before you run anything. Auto-indent, bracket matching, a symbol row above the keyboard you can customise, snippets you can add to, a formatter, and syntax-tree views for when you want to see exactly how a line parsed. Scan code out of a photo with on-device text recognition. Keep as many scripts as you like, search them, and open .py and .js files from Files or iCloud Drive.
FREE AND PREMIUM
Free includes a daily number of runs — a script run, a REPL entry, a trace or an assistant answer each count as one — and traces up to 200 steps. Premium removes the daily limit, traces whole programs, and unlocks export, formatting, code scanning, the coding fonts, custom snippets and keys, and watermark-free snapshots. Monthly, yearly, or a single lifetime purchase: your code runs on your device, so there is no server for us to keep paying for.
Your code stays on your device unless you choose a cloud runtime yourself.
PREMIUM OPTIONS
- Premium Monthly: auto-renewing subscription, billed monthly
- Premium Yearly: auto-renewing subscription, billed yearly
- Premium Lifetime: one-time purchase, not a subscription
Prices for your country are shown in the app before purchase. Payment is charged to your Apple ID at confirmation. Subscriptions renew automatically unless cancelled at least 24 hours before the period ends; manage or cancel them in your App Store account settings.
Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
Codecell Terms of Use: https://compilers.lodyworks.com/codecell/terms
Privacy Policy: https://compilers.lodyworks.com/codecell/privacy
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
The developer, LODYWORKS, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Used to Track You
The following data may be used to track you across apps and websites owned by other companies:
- Location
- Identifiers
- Usage Data
Data Linked to You
The following data may be collected and linked to your identity:
- Purchases
- Location
- Identifiers
- Usage Data
- Diagnostics
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- LODYWORKS
- Size
- 69.4 MB
- Category
- Developer Tools
- Compatibility
Requires iOS 16.0 or later.
- iPhone
Requires iOS 16.0 or later. - iPad
Requires iPadOS 16.0 or later. - Mac
Requires macOS 13.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- Contains
Advertising
- In-App Purchases
Yes
- Premium Lifetime $39.99
- Premium Yearly $19.99
- Premium Monthly $2.99
- Copyright
- © 2026 Lodyworks