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Chemvas is an open-source drawing tool for reaction schemes that you can rebuild. Every figure comes from an editable .cdxml file and one command, so it can be re-rendered at a journal column width after any change. A script or an AI agent can edit the same file through checked patches instead of rewriting it.
Open supported single-page ChemDraw XML (.cdxml) files from File > Open, edit
on the canvas, and use Save to write CDXML again. Import uses Chemvas drawing
styles while retaining native fragments, reaction references and vector objects.
Unsupported edits fail before replacing the file; see format limits.
What Chemvas is for
Reproducible publication schemes
render-documentexports SVG, PDF, PNG and CDXML without opening a window, fitted to a column width such as 84 mm or 174 mm.check-layoutreports common label collisions and content outside the sheet before you export. It does not check every pair of objects.- The publication recipes build finished figures from a script with a fixed bond length and font size, so every scheme in a manuscript has the same scale.
Agent editing you can check
inspect-documentlists every atom with a stable ID and every bond by its two atom IDs, and saved notes by their snapshot index, plus the SHA-256 of the file.apply-patchtakes a JSON patch of graph operations and note creation, movement, or content/style replacement. It refuses a patch written against different file bytes, can check a patch with--dry-runwithout writing anything, validates the whole document, and writes to a new file only. The input file is never modified.- Patches are checked for document structure, not for chemistry: element symbols and valence are not validated. Review the rendered figure before you use it.
Drawing by hand
- The desktop app draws structures, reaction arrows and labels, and provides alignment tools, autosave and session recovery. Drawings saved in the app work with every command above, and the reverse.
Current limits
Chemvas does not replace ChemDraw for file exchange. Inputs that Chemvas cannot represent exactly are refused with an error rather than drawn incorrectly.
- Opens:
.cdxml; SVG files that Chemvas exported with Editable Chemvas SVG checked (other SVG files cannot be opened); 2D MOL V2000 files within the subset Chemvas writes (bond orders 1–3, wedge and hash bonds, charges, radicals). - Refused: binary CDX and multipage CDXML, SDF and RXN files; MOL files with 3D coordinates, isotopes, aromatic bond type 4 or V3000.
Install
Requires Python 3.12+.
pip install chemvas
chemvas
Drawing, figure export and the script quickstart use this install. Chemvas has no optional chemistry extra.
For local Windows packaging, see the Windows packaging guide.
Quickstart: from a script or agent
chemvas compose-document scheme.json --output scheme.cdxml
chemvas inspect-document scheme.cdxml > inspection.json
chemvas apply-patch scheme.cdxml patch.json --dry-run
chemvas apply-patch scheme.cdxml patch.json --output revised.cdxml
chemvas check-layout revised.cdxml
chemvas render-document revised.cdxml --output scheme.svg --width-mm 174
scheme.json describes atoms, bonds, arrows and notes. patch.json carries the source_sha256 from inspection.json and the operations to apply. Each command writes a new file and refuses to overwrite an existing one, and check-layout exits with status 1 when it finds warnings. The formats and a worked example with images are in the Agent CLI guide.
Quickstart: in the desktop app
- Choose the Ring tool (
J) and click the left side of the canvas to place benzene. Choose Bond (X), drag one bond out from a ring atom to a new carbon, then drag a second bond from that carbon to a terminal atom. Hover the terminal atom, presso, then press Enter and set the label toOH. - Place a second benzene to the right. Drag one bond out from a ring atom to a new carbon, then drag a second bond from that carbon to a terminal atom. Hover the second bond and press
2so only that bond becomes a double bond, then hover the terminal atom and presso. Select the Arrow tool, drag between the structures, and double-click the arrow to add condition labels. - Select both molecules (Edit ▸ Select All) and align them (Edit ▸ Align ▸ Middle).
- Save the document (
.cdxml). Export via File ▸ Export Figure… → Plain SVG, Fit 2-column (174 mm).
For detailed instructions and example files, see the step-by-step guide.
Documentation
-
Browser adapter: experimental web editor available when running from a source checkout (
chemvas --ui web); omitted from installable wheel and sdist packages. Web source is experimental for future Leaf integration, not a standalone web product release. -
Drawing Tools & Shortcuts · MOL interchange · Image Objects · Document compatibility
-
Examples: Sample
.cdxmldocuments and the scripts that build the publication figures. -
Architecture · Contributing · Security · Changelog · Releasing · License (MIT)
Feedback and bug reports: GitHub Issues.
How this was built
I'm a chemist, not a programmer. AI coding agents write the code in this repository. I decide what Chemvas should do, record structural decisions as architecture decision records, keep saved drawings under a written compatibility policy, and set the checks a change must pass before it merges.
I don't review the code line by line, so a change is accepted on evidence, not on an agent's report that it works:
make checkruns lint, formatting and type checks, then runs each test file in its own process so Qt state cannot leak from one file into the next. CI runs the same per-file suite.- Chemvas does not write
machine.json. The calculation handoff and its project-local observation snapshot were removed with the chemistry backend (ADR 0055). Another project's decision to adopt a provider is outside this repository. - High-impact changes, such as the document format, undo and rollback, and figure export, get an independent adversarial review from a separate agent.
1 maintainer
Metadata
1 maintainer
Release files for chemvas 0.26.0
For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.
Source distribution (sdist)
| File | Size | Uploaded | Provenance | |
|---|---|---|---|---|
| chemvas-0.26.0.tar.gz | 745.0 kB | With provenance | Details |
Built distribution (wheel)
| File | Interpreter | ABI | Platform | Reset |
|---|---|---|---|---|
| chemvas-0.26.0-py3-none-any.whl | Python 3 | none | any | Details |
Total release size: 1.7 MB
Release files / chemvas-0.26.0.tar.gz
| Download URL | chemvas-0.26.0.tar.gz |
|---|---|
| Size | 745.0 kB |
| Tags | Source |
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SHA-256 checksum How to use checksums |
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Transparency logRelease files / chemvas-0.26.0-py3-none-any.whl
| Download URL | chemvas-0.26.0-py3-none-any.whl |
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| Size | 925.1 kB |
| Tags | Python 3 |
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SHA-256 checksum How to use checksums |
3275a107da389d87163ceec92f0605e01c196f72ee59541c441d24a0d13b4cba
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Yes |
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twine/7.0.0 CPython/3.13.14
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PyPI verified that this artifact, at this checksum, originated from the publisher listed below.
Signed by GitHub Actions, verified by PyPI on Oct 22, 2026.
Transparency logSecurity for chemvas 0.26.0
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Attestation for chemvas-0.26.0.tar.gz
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PyPI verified that this artifact, at this checksum, originated from the publisher listed below.
Signed by GitHub Actions, verified by PyPI on Oct 22, 2026.
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