Runs in your browser. Free, nothing to install.
A lightweight spreadsheet that edits CSV without breaking it
Leading zeros, encoding and line endings stay exactly as they were. Sort, filter and total your data with formulas. Your files never leave your computer.
- UTF-8, Shift_JIS & more
- Works offline
- No sign-in, no account
- Open source (MIT)
- Open a Shift_JIS CSV with CRLF line endings (it opens protected)
- Turn protection off and change one cell
- Only the edited cell is highlighted
- Save over the file — only that cell changed
Never breaks your CSV
Leading zeros, encoding and line endings stay as they were. Only the cells you edit change.
A real spreadsheet, kept light
Formulas, filters, conditional formatting and multiple sheets. Just the features you use most.
Your data stays with you
It runs entirely in your browser, so your files never need to be uploaded. One HTML file that works offline.
Spreadsheet
Total it, tidy it, compare it —
all in a lightweight spreadsheet.
It isn't meant to replace a full office suite. It's for working with the data in front of you, safely and quickly.
- Open a Shift_JIS CSV with CRLF line endings
- Type a formula into a cell
- Convert it to an RSF spreadsheet
- Calculated — the original CSV file stays as it was
- Select D2:D4 and use Fill Down to copy the formula
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Formulas and 55 functions
55 functions including SUMIFS, XLOOKUP, FILTER and UNIQUE, with references across sheets.
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Sort and filter
Narrow down to the rows you need and sort by up to eight columns at once.
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Data validation and conditional formatting
Limit what can be entered and color the cells that match a rule. Number formats, bold, colors and borders are there too.
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Totals with SQL
Query your tables with SQL and see the results in a read-only view.
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Compare two tables
Put two tabs side by side and see exactly what differs.
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Comments and version history
Leave notes on cells, review earlier versions and restore them.
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XLSX and JSON in and out
Import and export CSV, JSON and XLSX (exports contain values only).
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Notes and settings sheets
Keep Markdown, JSON, YAML and plain-text sheets in the same file.
CSV
Only the cells you edit change.
Every other byte stays the same.
No garbled text, no lost leading zeros. CSV files headed back into accounting, payroll or ordering systems are saved just as they were opened. Save without editing and you get a byte-for-byte identical file.
Under the hood, only the edited field's byte range is rewritten; everything else is written back byte for byte from the original file.
- Leading zeros: kept
- Encoding: kept
- Line endings: kept
- Delimiters and quotes: kept
- BOM and spaces: kept
- Broken parts: never auto-repaired
- Only the cells you edit change
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Encoding detection, and reopen with another
UTF-8 (with or without BOM), Shift_JIS / CP932 and EUC-JP are detected on open. If the guess is wrong, reopen the file with the encoding you choose. The original bytes do not change.
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Choose the format when you save
Save with Options lets you pick the encoding, BOM and line endings. If the chosen encoding cannot represent a character, the save stops first and tells you which cells.
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No conversion to numbers or dates
"0123", "2024-01-01" and 16-digit IDs all stay exactly as written.
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Broken CSV is diagnosed, not repaired
Unclosed quotes and field-count mismatches are listed with their rows and columns. Nothing is fixed automatically, and you decide whether to open the file.
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Files open read-only
Existing files open protected, so nothing changes by accident. To make an edit, turn protection off with Edit in the status bar.
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Japanese input and the keyboard
While you compose Japanese text, Enter and the arrow keys belong to the input method; the cell only receives the confirmed text. Every menu command also works from the keyboard.
Use cases
For the everyday trouble with business CSV files.
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Accounting and tax
Account codes lose their leading zero and the import fails
Codes stay as text, so you can fix journal and filing CSVs without disturbing the required columns or the Shift_JIS encoding.
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HR and payroll
Employee IDs and times turn into numbers or dates
Values are never type-inferred, so leading zeros in employee IDs and postal codes, and "HH:mm" times, stay exactly as written.
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Orders and e-commerce
A barcode number shows up as 4.9E+12
Long numbers are never treated as numbers, so they never switch to scientific notation. Your partner’s column order, delimiter and quoting stay as they were.
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Totals and checks
You want to total an exported CSV to check it
Convert it to an RSF spreadsheet and total it with formulas, filters or SQL. The original CSV file is not changed.
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Troubleshooting
A CSV is broken and you can’t tell where
See unclosed quotes and mismatched field counts with their row and column, without any automatic repair.
Privacy & security
Keep confidential data on your own computer.
Nothing uploaded, nothing executed, nothing hidden. Everything you need to check it against your company's policies.
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Nothing is uploaded
Files are processed inside your browser. Nothing is sent anywhere unless you choose to use Google Drive.
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No scripts are run
Cell contents are always shown as plain text. HTML or scripts hidden in a file never run.
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Open source
Open source under the MIT license, so anyone can inspect it. Distributed as a single HTML file.
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The offline version never connects
The downloadable offline version blocks every network connection with its Content Security Policy.
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Few dependencies, known origins
Third-party libraries are kept to a minimum and no install scripts are run. Releases come with SHA-256 checksums, an SBOM and signed build provenance.
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Google Drive, only when you use it
The web app talks to Google only when you choose Open from Drive or Save to Drive. It can reach only the files opened or created through this feature (drive.file).
Compare
How it differs from a typical spreadsheet app
It isn't meant to replace a full office suite. The difference is in how a CSV is opened and saved, and in how quickly you can start.
| What to compare | Typical spreadsheet apps | Refrain Sheet |
|---|---|---|
| Saving without any edits | Depending on how the file is opened, encoding, quotes or line endings may change | Byte-for-byte identical to the original |
| Fixing a single cell | Depends on the product and settings | Every byte outside the edited cell is kept |
| Leading zeros, dates, long IDs | May be converted to numbers or dates for display or calculation | Stay exactly as written |
| Shift_JIS CSV files | Text may be garbled depending on how the file is opened | Encoding detected and kept on save |
| Broken CSV files | Depends on the product | Opened as they are, with the problems pointed out |
| Formulas, functions, formatting | A very wide range | 55 functions and the formatting you use most, in an RSF spreadsheet |
| Getting started | May need an install or an account | Just open it in a browser — no sign-in, no account |
Typical spreadsheet apps behave differently by product, version and settings. Refrain Sheet's behavior can be checked against its README and test suite.
FAQ
Questions
Is it free?
Yes. It is open source under the MIT license, with no account needed. Use the web app in your browser, or download the offline version.
Do I need to sign in or create an account?
No. Open the web app in your browser and start right away. You are asked to sign in to a Google account only when you use the Google Drive integration.
Is it a replacement for Excel?
No — it has a different purpose. Refrain Sheet is a lightweight spreadsheet for handling your data without breaking it, and Excel compatibility is not claimed. CSV files are edited as they are; for formulas and formatting you convert to an RSF spreadsheet.
How do I keep leading zeros in a CSV file?
You don’t have to do anything. Values are never type-inferred, so "0123" or a number of 16 digits or more is handled as the text it is written as and written back unchanged on save. Whether the receiving system accepts that value depends on that system, so check its specification beforehand.
Will a Shift_JIS CSV turn into garbled text?
No. The encoding is detected when the file opens, and the file is written back in the same encoding; if the detection is wrong, you can reopen the file with a chosen encoding. Supported encodings are UTF-8 (with or without BOM), Shift_JIS / CP932 and EUC-JP. UTF-16 and ISO-2022-JP are not supported; such files still open with a best-effort interpretation and a warning, and their bytes remain untouched.
Can I add formulas or colors while keeping the file a CSV?
Not in the CSV itself. Formulas and formatting (bold, color, borders) are RSF spreadsheet features that require an explicit conversion to RSF. The original CSV file is not changed by the conversion, and formatting never changes a cell’s value, formula results or CSV export.
Is my data sent anywhere?
Not during normal editing. Files are read inside the browser and saved back to your own device. Only when you use the Google Drive integration in the web app are files exchanged, at your request, directly between your browser and Google Drive.
Can I use it on a computer that isn’t connected to the internet?
Yes. Download the offline version (ZIP) from the releases page, unzip it and open index.html in your browser. It works from file:// and never connects to the network.
Can I use it on a phone or tablet?
Yes, in the browser. On narrow screens and touch devices, text and controls are shown at larger, touch-friendly sizes.
Is there an English interface or a dark theme?
Yes. The interface switches between Japanese and English, and the theme can follow your system setting or be set to light or dark. Display settings never change the contents of your files.
How large a file can it open?
The default limit is 512 MiB (adjustable from 16 MiB to 2 GiB) and oversized files are refused before their bytes are read. Rendering is virtualized, but files of hundreds of megabytes can still feel slow.
Can I open a broken CSV file?
Yes. Problems such as unclosed quotes or field-count mismatches are listed with their rows and columns, and you choose whether to open the file without any automatic repair. Broken regions are kept byte-for-byte unless you edit them, but there is no guarantee the receiving system will accept the damaged data.
Can it overwrite the original file?
In Chromium-based browsers (Chrome, Edge and others), yes. Firefox and Safari save by downloading instead, and the app tells you which kind of save happened.
Does this introduction page use analytics?
Only this introduction page (refrain-sheet.com) may use Google Analytics, to measure visits. It loads only if you choose "Accept" in the consent banner at the bottom of the page, and you can change that choice anytime from "Cookie settings" in the footer. The app itself (app.refrain-sheet.com), where you edit CSVs, is served separately and contains no analytics.
Get started in three steps.
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Open it in your browser
No install, no sign-in, no account.
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Drag and drop a CSV file
The encoding is checked as it opens. Your file never leaves your computer.
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Edit and save
Only what you changed is changed.