Reactio Draw

A free chemical structure and reaction editor for organic chemists. Draw with the mouse or the keyboard, keep a reagent table for every reaction (equivalents, masses, volumes, yield), predict NMR, and move drawings into Word and PowerPoint or to and from other chemistry editors as CDXML and CDX files. It also helps you check HRMS data.

▶ Open in the browser	⬇ Apps for Windows, Mac and Linux	📖 Guide (PDF)
nothing to install	work fully offline	every function and button explained

reactio-video.mp4

What it does

Drawing	drawing with the mouse as usual, with alignment guides while you drag (edges and centres snap to nearby molecules, arrows and captions); adding groups with hotkeys at the hotspot (the atom or bond under the pointer, marked green; after each key it moves on to the new group, so a chain or a substituted ring is typed key after key, and the arrow keys move it); your own labels and templates; bold or italic single characters (tBu), tBu / iPr prefixes plain, italic or italic superscript in one click; reaction and mechanism arrows, brackets and a charge corner, shapes, sandwich complexes, 3D rotation and 3D shapes, orbitals; Merge structures joins structures drawn on top of each other
Reactions	a reagent table on the sheet or below it, for the selected reaction or the whole sheet: roles, limiting reagent, equivalents, masses, volumes, concentrations, yield, conditions; reagents written as text (MeMgBr, K2CO3) are counted too; multistep schemes; compound numbers that renumber themselves
Analysis	formula, molecular weight, exact mass, m/z, isotope pattern, elemental analysis, SMILES, InChI and InChIKey (offline), ¹H/¹³C/¹⁹F/³¹P NMR prediction from measured spectra; structure checks as you draw (valence, atoms on top of each other, stray bonds, wedges), each kind can be switched off
Names	common names everywhere; systematic names to structures (OPSIN) and structures to IUPAC names (openclatura) in the apps
Files	its own .reactio documents; CDXML, CDX, MOL and SDF (V2000 and V3000), RXN, SMILES and CXSMILES, ORD; pictures as SVG, PNG, EPS, TIFF; pictures on the sheet travel in CDXML and CDX; Word and PowerPoint
Word and PowerPoint	Ctrl+C → Ctrl+V into Word or PowerPoint on Windows and on Mac. Double-click a drawing in Word to edit it, on Windows and on Mac alike; Save in Reactio Draw puts the new drawing back in its place (Edit drawing on the Reactio Draw tab does the same). A document can travel between the two: a drawing put in on Windows is an object, one put in on a Mac a picture, so on the other system double-click does not open it — copy it instead (Ctrl+C in Word, Ctrl+V in Reactio Draw) or use Open in Reactio Draw on the tab, and it comes back complete: structures, reagent table, roles and conditions, nothing lost. The tab (Windows and Mac) also makes plain vector pictures without Reactio Draw data, puts all structures of a document into one CDXML file, and marks pictures that hold Reactio Draw data with hidden, non-printing marks
Charts	sensitivity screens — the radar diagrams of the condition-based sensitivity assessment of Glorius and co-workers (Angew. Chem. Int. Ed. 2019, 58, 8572), editable on the sheet; product ratio pie and ring charts
Working fast	scrolling in every direction (two fingers, or Shift+wheel sideways) and zoom to the pointer; a hotkey for every button and command, all reassignable, with search by name or by key; your own templates and labels on keys
API and command line	a local API for scripts (Python, R, curl) in the desktop apps; a command line, reactio, that renders, converts and checks files without opening a window (Command line.txt); and the same commands for web pages that embed the editor (EMBEDDING.md)
Styles	ACS, RSC, Nature, Angewandte and more, colour themes (one of them color-blind safe), dark sheets
Light	the whole editor is one web page of 4.0 MB (about 1.4 MB over the network; 6.2 MB as a single offline file with the NMR tables), with no server and nothing to install; the apps are about 20–28 MB to download. The NMR tables (2.2 MB) come only when you first predict a spectrum. For comparison, the Ketcher npm package is about 110 MB and Kekule.js about 42 MB

Download

Browser	the link above, or index.html from this repository: open it in Chrome, Edge, Safari or Firefox
Windows 11	ReactioDraw-Windows-x64.zip (or -ARM.zip): unzip, run ReactioDraw.exe
Mac	ReactioDraw-Mac.zip: double-click Install Reactio Draw.command (builds the app on your Mac)
Linux	ReactioDraw-Linux-x64.tar.gz (or -ARM): unpack, run ./install.sh; needs WebKitGTK

The apps add naming (OPSIN, openclatura), Word and PowerPoint objects (Windows), the Reactio Draw tab in Word (Windows and Mac), a local API for scripts and the reactio command line.

On your own site: Reactio Draw can be embedded in any web page (an ELN, a course page, a search form) and driven from its JavaScript: see EMBEDDING.md and the working example in examples/embed.html.

Tested on: Windows 11 Enterprise 26H2, macOS Sequoia 15.7.4, Ubuntu 24.04.2 LTS. Other recent versions are likely to work but have not been checked; reports are welcome.

Privacy

Reactio Draw makes no network requests of its own: no accounts, no tracking, no analytics, no fonts or scripts from other sites. Drawings, settings, labels and templates stay in your browser or on your computer. The only downloads are these: the web version is loaded from its site like any web page, and there the NMR tables are downloaded only when you agree, on the first Predict, and kept in the browser (clearing the site's data removes them); a link you click (GitHub, a DOI) opens in your browser. The apps download nothing.

NMR prediction is an estimate from nmrshiftdb2 data, not a measured spectrum; the copied text says where the data come from, as the nmrshiftdb2 Database License asks.

Source

Folder	What
index.html	the whole program in one file (drawing, analysis, NMR prediction); the apps and the download use it
web/	the web version GitHub Pages serves, made from index.html by tools/make_web.py: the NMR tables are a separate file, downloaded on the first Predict
windows-app/	Windows app: Go + WebView2 window, OLE server for Word and PowerPoint, local API
macapp/	Mac app: Swift window around the page, installers, naming helper
linux-app/	Linux app: Go window with GTK and WebKitGTK, local API
data/nmr/	how the NMR shift tables were built from nmrshiftdb2
word-addin/	the Reactio Draw tab for Word (Reactio Draw.dotm) and the script and macros it is built from
examples/	embed.html: Reactio Draw embedded in another page (see EMBEDDING.md)
docs/	the guide Reactio Draw - Getting started.pdf, the hotkey chart Reactio Draw - Hotkeys.reactio the README picture overview.png and the hotkey chart as a picture
tools/	scripts that make the web version, the InChI WebAssembly build, the README picture, the hotkey chart and the Windows resources
LICENSES/	the licences of the third-party parts (see THIRD-PARTY-NOTICES.md)

How it was written

Reactio Draw is written from scratch for this project. No program was decompiled or disassembled, and no code from commercial chemistry software is used. File formats are implemented from published descriptions and open-source projects, each named in Credits and THIRD-PARTY-NOTICES.md:

• CDX and CDXML: the CDX property table from ReShiki, which takes it from the published CDX documentation of CambridgeSoft (the CDX SDK, archived by the IUPAC FAIRSpec project). Every code in it is also defined in Revvity's own open-source ChemDraw format library (BSD-3-Clause), the stoichiometry grid of ChemDraw (objects 0x8022–0x8024, properties 0x1200–0x1208) included.
• MOL, SDF and RXN: the CTfile format description.
• Word and PowerPoint objects: Microsoft's published specifications (Office Open XML / ECMA-376, compound files [MS-CFB], OLE objects [MS-OLEDS], RTF).
• The Reactio Draw tab in Word (word-addin/): a template written by make_dotm.py from Microsoft's published specifications of the VBA project [MS-OVBA] and of Office's custom tabs [MS-CUSTOMUI]; Word compiles the macros (ReactioDraw.bas) from their source.

In Word and PowerPoint the drawing is an object of its own type, ReactioDraw.Drawing.1; it does not pose as another program's object.

Building

• Web: nothing to build; index.html is the program. For a site, python3 tools/make_web.py writes web/ (the page without the NMR tables, and the tables beside it).
• Windows (Go 1.24+): copy index.html into windows-app/, then in windows-app/: GOOS=windows GOARCH=amd64 GOFLAGS=-mod=mod go build -trimpath -ldflags "-H windowsgui" -o ReactioDraw.exe (GOARCH=arm64 … -o ReactioDraw-ARM.exe), and the command line: GOOS=windows GOARCH=amd64 GOFLAGS=-mod=mod go build -trimpath -o reactio.exe ./reactio. Ship tools/, WebView2Loader-*.dll and word-addin/Reactio Draw.dotm (the Word tab) beside the exe.
• Linux (Go 1.24+, no C compiler needed): linux-app/build.sh. Ship tools/ (with windows-app/tools/opsin-2.9.0.jar) and the reactio script beside it.
• Mac: copy index.html to macapp/index.html, windows-app/tools/opsin-2.9.0.jar to macapp/opsin.jar and word-addin/Reactio Draw.dotm (the Word tab) into macapp/, then run macapp/Install Reactio Draw.command (needs Apple's Command Line Tools).

All libraries are in the repository (third_party/ folders), so the builds work offline.

How to cite

If Reactio Draw helped your work, please cite it: Sakharov, P. Reactio Draw, Zenodo, doi:10.5281/zenodo.23547490. This DOI always leads to the latest version; each release also has a DOI of its own (1.3: 10.5281/zenodo.23547491). GitHub's Cite this repository button (on the right of the repository page) gives the reference in APA and BibTeX, from CITATION.cff.

Licence

Copyright © 2026 Pavel Sakharov.

Reactio Draw is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. See LICENSE.

Anyone who distributes Reactio Draw or a modified version, or offers a modified version to others over a network, must make its complete source code available under the same licence. If you would like to use Reactio Draw code in a project under another licence, such as MIT, open an issue: as the author, I can grant a separate licence. Drawings, files and schemes you make with the program are yours; the licence does not cover them.

Third-party components and their licences: THIRD-PARTY-NOTICES.md and the LICENSES/ folder.

Credits

Made with the help of Claude (Anthropic). Questions, ideas and bug reports: Issues.