EngiPad

Free, open-source calculation notebook for engineers: physical units, symbolic math, matrices and plots with instant LaTeX output. Several worksheets in one file, print or export to pdflatex-ready .tex. Runs locally on Windows and Linux, no cloud, no account.

• Calculate with physical units (10'kg, 5'W/(m*K), 2'bar | Pa) and get dimension checks for free
• Symbolic math: derivatives, integrals, equations, sums, products, limits
• Vectors, matrices and plots
• Results typeset with MathJax while you type (optional live update)
• Worksheets: several named sheets in one file that read each other's values (Loads::F)
• Undo/Redo: buttons and Ctrl+Z/Ctrl+Y for the whole workbook (also sheet add/delete/rename), usable on tablets
• Pictures: show a PNG sketch in the output with picture("beam", width=400, align=center); it is stored inside the saved text file
• Print or export the sheet(s) as a standalone .tex document (with plots and pictures)

The interface consists of a text editor on the left and a LaTeX/plot output area on the right.

Download

Download for Windows (.exe)

Download for Linux (.AppImage)

Screenshot

User guide

The complete guide (input syntax, units, worksheets, settings, printing and export) is in USER_GUIDE.md.

Features

• Web UI using Flask, HTML/CSS/JavaScript and MathJax
• Expressions are parsed by a small, purpose-built parser and evaluated through a fixed function whitelist — no eval()/sympify() is ever run on user input (see Security)
• SymPy integration for symbolic expressions (diff, integrate, Eq, solve, csolve, nsolve, sum, prod, lim), numeric evaluation and symbolic display mode (:=)
• Unit system: apostrophe syntax (10'J, 5'm), dimension checks, automatic unit simplification, and explicit target units with | unit — any product/quotient/power of known units (| kWh, | J/(kg*K))
• Vectors and matrices: vec, mat, det, inv, dot, cross, eigenvals, indexing like sol[0], …
• Plotting with plot(f, x, xmin, xmax)
• Pictures: picture("name", width=300, align=left) shows a PNG (button Insert image). The pictures are stored in the saved text file (Base64 blocks at its end), appear in the printout and in the LaTeX export; at most 10 pictures, total size limited by a setting (1–3 MB)
• Worksheets: ##Name sheets in one text file, tabs below the editor (add, rename by double-click, delete), read-only cross-sheet references Sheet::var
• Live update on Enter (optional) and Ctrl+Enter to calculate
• Text lines ("bold", 'plain', spaces preserved) and # comments
• Greek variables and accent notation (Q__dot, Q__bar, Q__hat, Q__tilde)
• Settings: rounding precision, font size, unit size, sheet-prefix size, print/export all sheets, timeout, image limit, live update
• Print layout with sheet name in the page header; export to pdflatex-compilable .tex (or .zip with plots and pictures), one sheet or all sheets
• Configurable computation timeout protects against very expensive input

Security

Expressions are evaluated through a custom recursive-descent parser (parsing/) and a small AST-to-SymPy bridge (mathlib/sympy_bridge.py) that only ever calls a fixed whitelist of functions (mathlib/functions.py). Unknown function names become inert symbolic placeholders rather than being executed. No user input is ever passed to Python's eval() or SymPy's sympify()/parse_expr().

Pictures are accepted as PNG only and are checked by their bytes (signature, header, end marker) with hard limits for size and pixel count before anything decodes them, so a small file that would expand to gigabytes is refused. Picture names are restricted to letters, digits and underscore, pictures are never read from a file path on the server, and the browser shows them only as <img> (no SVG, no scripts). The LaTeX export checks everything again on the server.

Each computation additionally runs in a separate process with a hard timeout (core/safe_runner.py, default 10 s) so a single expensive or hanging input can't tie up the server.

The bundled run.py binds to 127.0.0.1 by default — if you expose this on a network beyond localhost, review app.py/run.py first. Behind a reverse proxy, allow request bodies of about 8 MB (e.g. nginx client_max_body_size 8m;), otherwise the LaTeX export of a sheet with several pictures is refused by the proxy.

Requirements

• Python 3
• Python packages: see requirements.txt (Flask, Jinja2, sympy, matplotlib, numpy)
• For running the test suite: see requirements-dev.txt (pytest)

pip install -r requirements.txt

Running from source

python run.py

The application runs on http://127.0.0.1:5000. As a normal Python script it starts the Flask development server; as a packaged executable it also opens the browser automatically.

Optional environment variable: ENGIPAD_LIVE_DEFAULT=1 or 0 sets whether live update is on by default (on in the local version, off on a server).

Running the tests

pip install -r requirements.txt -r requirements-dev.txt
pytest

Building a standalone binary

Ready-made builds are available under Download. To build your own Linux AppImage or Windows executable/installer, see BUILDING.md.

Credits

• Author: Prof. Dr. Peter Stein
• Coding: Claude (Anthropic) — the implementation, architecture, tests, and documentation were written with Claude as an AI coding assistant.

License

This project is licensed under the GNU General Public License v3.0 (GPL-3.0). See the LICENSE file for details.

This project uses ICONS from Lucide Icons