Strict compiler
Tokenize, parse, validate, and compile structured pseudocode with line and column diagnostics that point at the real mistake.
Free and 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.
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 generated flowchart to reason about decisions, loops, and processes visually.
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 GPL v3. No trackers, no paywall.
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.
learn while you build
Docs that sit next to the editor.
Short, practical guides for the syntax the compiler accepts. Read one, then try it in the editor a click away.
Open the manualGuide 1
Getting started with Pseudo Build
Open the browser editor, write your first pseudocode program, compile it, and run it directly in the browser.
Guide 2Pseudocode syntax reference
Reference the core pseudocode syntax supported by the browser compiler, including assignment, conditions, loops, arrays, and output.
Guide 3Variables, input, and output
Learn how Pseudo Build handles declarations, assignment, INPUT prompts, and OUTPUT statements.
Guide 4IF, THEN, ELSE selection
Use IF statements to branch pseudocode programs based on comparisons and Boolean expressions.
blog
Notes on writing better pseudocode.
5 min read
IGCSE pseudocode basics: a practical starting point
A compact guide to declarations, assignment, input, output, and the habits that make pseudocode easier to trace.
6 min read
How to trace pseudocode without guessing
Use a repeatable trace-table process to follow variables, branches, and loop updates.
4 min read
Choosing between FOR, WHILE, and REPEAT UNTIL
Learn a simple decision rule for picking the right pseudocode loop structure.
questions
Answers before you ask.
What is Pseudo Build?+
Pseudo Build is a free and open-source pseudo code editor and compiler. The editor, compiler, runner, flowchart view, manual, and workspace tools all run in the browser app.
Can I run pseudocode in the browser?+
Yes. Pseudo Build compiles supported pseudocode to an AST and runs it in the browser runtime, including interactive INPUT prompts.
Does the browser version save my work?+
Local development saves to browser storage. On pseudo.build, 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). Pseudo Build 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 Pseudo Build really free and open source?+
Yes. Pseudo Build is free to use and the source code is published under the GNU GPL v3 on GitHub. 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.
Open source
Read the code. Run it yourself. Make it yours.
Pseudo Build is licensed under the GNU GPL v3. Clone the repository, run it locally, file issues, and send pull requests.