Strict compiler
Tokenize, parse, validate, and compile structured pseudocode with line and column diagnostics that point at the real mistake.
Free forever · Open source
Build pseudo code
that actually runs.
Free and open-source pseudo code editor and compiler. Write structured pseudocode, compile it with real diagnostics, and run it in your browser. Built for Computer Science students. Build your pseudo code project freely and creatively.
Free forever. No account needed. Sign in only if you want cloud sync.
what you get
An editor, a compiler, and a runtime. Nothing to install.
Runs in the browser
A Rust runtime compiled to WebAssembly executes your program on your machine, including interactive INPUT prompts.
Flowchart view
Switch between source and a flowchart of the same program. Edit either one and the other follows.
Debug with intent
Read the first diagnostic, fix it, run again. Diagnostics are ordered so cascading errors do not bury the cause.
Workspaces that follow you
Work in memory, in local browser storage, or sign in to sync a multi-file workspace across devices.
Open and auditable
Every line of the editor, compiler, and runtime is published under the Apache License 2.0. Read the code, run your own copy, or contribute a fix.
built for the classroom
Practise the pseudocode your exam actually uses.
The syntax follows the Cambridge pseudocode conventions used in IGCSE, O Level, and AS & A Level Computer Science papers, so what you practise here is what you write on paper.
Teachers: nothing to install on school machines, no accounts to manage, and the whole project is open source.
Open a random practice questionIGCSE Computer Science (0478 / 0984)
Variables, IF and CASE selection, FOR, WHILE and REPEAT loops, arrays, and string handling in the exam's own notation.
O Level Computer Science (2210)
The same pseudocode conventions and the same trace-table habits, with instant feedback when a block is not closed.
AS & A Level Computer Science (9618)
Procedures, functions, CASE, and text file handling for the longer algorithm questions.
Lesson
Visual lessons that sit next to the editor.
Every IGCSE Computer Science topic, from binary to logic gates, with diagrams you can click and step through. Read a lesson, then try the pseudocode in the editor a click away.
Explore the lessonsData representation
Binary, denary, and hexadecimal
Why computers count in binary, how to convert between binary, denary, and hex, and where hex is used.
Hardware
The CPU and the fetch-decode-execute cycle
Von Neumann architecture, the CPU's registers and buses, the fetch-decode-execute cycle, and what makes a CPU faster.
Programming
Iteration with FOR, WHILE, and REPEAT
Count-controlled, pre-condition, and post-condition loops, when to use each one, and how to avoid endless loops.
Boolean logic
Logic gates and truth tables
The six logic gates, NOT, AND, OR, NAND, NOR, and XOR, with their symbols and truth tables.
blog
Notes on writing better pseudocode.
5 min read
Flowchart mode is out of beta
Draw any program as a flowchart, edit it in either view, and watch a run move block by block.
4 min read
The docs are now a full IGCSE Computer Science course
32 visual lessons follow the Cambridge 0478 syllabus across both papers, from binary to Boolean logic, with diagrams you can click.
4 min read
Write pseudocode the way your exam board does
Settings switches the compiler between Cambridge IGCSE, Cambridge A Level, IB, OCR, and AQA notation.
questions
Answers before you ask.
What is PseudoEditor?+
PseudoEditor is a free and open-source pseudo code editor and compiler. The editor, compiler, runner, flowchart view, docs, and workspace tools all run in the browser app.
Can I run pseudocode in the browser?+
Yes. PseudoEditor compiles supported pseudocode to an AST and runs it in the browser runtime, including interactive INPUT prompts.
What is a pseudocode compiler or pseudo emulator?+
A pseudocode compiler checks a defined pseudocode syntax before execution. A pseudocode runner, sometimes called a pseudo emulator, executes those instructions so you can test an algorithm. PseudoEditor includes both, with error diagnostics, interactive input, and program output. Select your exam board in Settings because pseudocode has no single universal syntax.
Do I need Visual Studio Code to run pseudocode?+
No. PseudoEditor is a standalone browser app with its own pseudocode compiler and runtime. Open the editor, create a file, select your exam syntax, and choose Run. You do not need to install Visual Studio Code or an extension.
Does the browser version save my work?+
Local development saves to browser storage. On pseudoeditor.dev, signed-in users can save workspaces with Clerk authentication and Convex cloud sync.
Is this only for IGCSE Computer Science?+
No. Settings lets you switch between Cambridge IGCSE, Cambridge AS and A Level, IB Diploma Programme, OCR GCSE, and AQA GCSE notation. The compiler, highlighter, and completions follow the syntax you pick.
Which exam boards does the pseudocode follow?+
The syntax follows the Cambridge International pseudocode guide used in IGCSE Computer Science (0478 and 0984), O Level Computer Science (2210), and AS and A Level Computer Science (9618). PseudoEditor is an independent project and is not affiliated with or endorsed by Cambridge.
Do I need to install anything?+
No. The editor, compiler, and runtime load in any modern browser on a laptop, Chromebook, or tablet. Nothing is installed and nothing needs to be approved by school IT.
Is PseudoEditor really free? Will it stay free?+
Yes, and it always will be. There is no paid plan, no trial, and no premium tier waiting down the road. PseudoEditor is also open source: the code is published under the Apache License 2.0 on GitHub, so you can read it, run it yourself, and contribute.
Can I practise random exam-style questions?+
Yes. The practice page draws an original IGCSE, O Level, or A Level style task at random. You can filter by topic, open a starter file in the editor, and run your answer in the browser.
Free forever, open source
Free today. Free forever. Open source, always.
PseudoEditor costs nothing and always will. There is no paid plan, no trial, and no feature held back for later. The editor, compiler, and runtime are open source under the Apache License 2.0, so you can read the code, run it yourself, and send pull requests.