Refrain Sheet
A local-first, format-preserving CSV and spreadsheet editor.
Web App · Releases
Refrain Sheet is a local-first, offline CSV and spreadsheet editor that runs
directly from a local HTML file. It preserves CSV files as faithfully as
possible while supporting lightweight spreadsheet editing through RSF.
Open index.html directly in a browser; no installation, server, account,
or network connection is required.
“Refrain” means refraining from touching your original CSV unnecessarily.
Edit field values while preserving everything else as faithfully as possible:
delimiters, quoting, surrounding whitespace, line endings, encodings, byte
order marks, undecodable bytes, and malformed regions. Spreadsheet-only
features (formulas, structural edits, per-document metadata) are provided
through RSF (Refrain Sheet Format). The exact byte-preservation
guarantee and its documented exceptions are in
knowledge/domains/csv-preservation-guarantee.md.
ローカルで動く、書式保持CSV・スプレッドシートエディタです。
CSVのフィールド値だけを編集し、区切り文字、引用符、空白、改行コード、文字コード、
BOM、不正なCSV領域などを可能な限り保持します。
CHANGELOG.md tracks notable user-visible changes by version.
The version is defined in package.json and surfaced through the app
(Help > About / Keyboard Shortcuts shows it), the metadata written into
saved .rsf files, and the release artifact name.
Detailed knowledge
This README is an entry point, not a reference manual. Durable, detailed
knowledge — architecture, security, performance, the RSF file format,
core spreadsheet/CSV domain behavior, and UI/interaction behavior — lives
in the knowledge/
OKF v0.2
bundle:
- Architecture — layers, dependency
direction, the formula engine's structure, and cross-cutting invariants.
- Operations — the security threat model,
supply-chain controls, and performance principles/measurements.
- Formats — the full
.rsf file
specification (Zstandard-compressed JSON).
- Domains — core spreadsheet/CSV-editor
behavior: the preservation guarantee, workbook/worksheet lifecycle,
formulas and references, functions and errors, dynamic arrays, undo/
redo, import/export/conversion, and version history.
- UI — interaction and presentation behavior:
editing and IME safety, selection/navigation, copy/paste/fill, find and
replace, column resize/auto-fit, view formatting and dockable panels,
tabs, mobile/touch, accessibility, and theming.
Features
- Byte-identical CSV preservation. An unedited save writes the loaded
bytes verbatim; edits reserialize only the changed field ranges.
Supports UTF-8, Shift_JIS/CP932, and EUC-JP.
- Spreadsheet mode via RSF. Formulas (55 functions, cross-sheet
references, dynamic arrays), multiple worksheets (including Markdown/
JSON/YAML/plain-text worksheets), filtering, sorting, data validation,
conditional formatting, cell formatting, a local read-only SQL query
view, and in-file version history with restore/preview.
- Import and export. CSV, JSON, and XLSX import; CSV, JSON, and XLSX
export — each an explicit, lossy (values-only) conversion. Markdown,
JSON, YAML, and text files also open directly in their editors and save
back to the same file.
- Keyboard, mobile/touch, and accessibility support. IME-safe editing
from the first keystroke, full keyboard operability, ARIA labeling
throughout, and a touch-adapted mobile layout.
- Light / Dark / Hybrid themes. System default, Light, Dark, or
Hybrid (the UI follows the system color-scheme preference while the
spreadsheet grid stays light) — Hybrid is the default for new
installs.
- Offline and secure by design. No runtime network access, no
eval/dynamic code, a sandboxed formula engine, and an embedded
WebAssembly core that is never fetched.
CSV injection warning
Values beginning with =, +, -, or @ may be interpreted as
formulas by spreadsheet software (Excel, LibreOffice, Google Sheets)
when the saved CSV is opened there. In keeping with the Refrain
principle, this application never silently modifies, escapes, or
prefixes your values as a mitigation — be careful when opening CSV files
from untrusted sources in spreadsheet software.
Running via file://
The build output is completely static and self-contained:
- Get
dist/ (build it yourself or download a release ZIP).
- Open
dist/index.html (or index.html inside the extracted ZIP)
directly in a browser — double-click it or press Ctrl+O in the browser.
There is no dev server requirement, no backend, no browser extension, no
CDN, and no network access of any kind. The bundle is a classic (non-module)
script specifically so it works under file:// in Chromium, and a
restrictive Content Security Policy (connect-src 'none', no http:/https:
source anywhere) blocks all outgoing connections.
Browser support
| Capability | Chrome / Edge (Chromium) | Firefox | Safari |
|---|
Run from file:// | ✔ | ✔ | ✔ |
| Overwrite save (File System Access API) | ✔ (with permission prompt) | ✘ → download save | ✘ → download save |
| Writable handle from drag & drop | ✔ | ✘ | ✘ |
Development
Requirements: Node.js ≥ 20 and npm, or Docker.
This is the beginning of the README. Read the rest at the original. Read the full README ↗
