Formula-like prefixes
Prefixes risky markers with your selected escape to reduce execution risk on initial spreadsheet import.
CSV hygiene, before production
Clean risky CSVs.
Keep the rows private.
Detect formula-like prefixes, duplicate records, empty rows, messy headers, and stray whitespace in one deterministic pass.
文件不离开浏览器。无需账号、不上传文件内容，清理后立即下载。
- 0 file bytes uploaded
- 10 MB maximum
- No account
Local workbench
Inspect a CSV
Adds an apostrophe before risky markers. The apostrophe stays in data, so downstream tools must accept or strip it. Excel may remove its escape behavior after save/reopen. Negative numbers are also prefixed.
Waiting for a CSV.
Cleanup ready
0 cleaned rows
Apostrophe-prefixed export
- Formula-like segments changed
- 0
- Duplicates removed
- 0
- Empty rows removed
- 0
- Cells trimmed
- 0
- Headers normalized
- 0
Useful? Star the project or share feedback. Never attach a private CSV.
Five deterministic checks
Small CSV defects become expensive downstream.
CSV Guard makes conservative, repeatable fixes and reports an exact count for every change before you download.
Duplicate rows
Removes byte-equivalent records after leading and trailing whitespace cleanup.
Empty records
Drops rows with no meaningful value across every detected column.
Messy headers
Normalizes field names and resolves collisions without discarding columns.
Stray whitespace
Trims invisible edges that break joins, comparisons, and imports.
The risk hiding in plain text
A CSV cell can become executable when a spreadsheet opens it.
If a cell’s first effective character is =, +,
-, or @, spreadsheet software may interpret it as
a formula. CSV Guard prefixes every such segment—including one exposed
after a comma, semicolon, tab, or pipe—with the mode you select.
No universal CSV prefix strategy works across every spreadsheet and downstream
consumer. Excel can remove apostrophe-based escaping after you save and reopen a
file; the Excel review mode leaves a real tab and an apostrophe in the data. Re-clean
untrusted exports before reopening them. Both modes also prefix negative numbers such as -42,
changing their inferred type. See the
OWASP CSV Injection guidance.
Compare apostrophe and layered tab prefixes, then test your Excel workflow →
Choose by destination
| Mode | Best fit | Known trade-off |
|---|---|---|
| Apostrophe prefix | Downstream accepts or strips apostrophe | Apostrophe stays in data; escape may not survive Excel save/reopen |
| Excel review tab + apostrophe | One-time human review in Excel | Both prefixes stay in data and may disrupt imports |
Risky input
=HYPERLINK("https://example.test")Apostrophe-prefixed output
'=HYPERLINK("https://example.test")Browser safety envelope
Hard limits bound parser work.
Large inputs can still be memory-intensive, especially on mobile devices.
- File or pasted text
- 10 MB
- Data rows
- 100,000
- Columns
- 5,000
- Normalized cells
- 500,000
- Characters per field
- 2,000,000
Privacy by architecture
Your rows never touch an application server.
Parsing, cleanup, preview, and export all run inside this browser tab. This static edition has no analytics endpoint, no account system, and a browser policy that blocks background network connections.
GitHub Pages serves the initial HTML, CSS, and JavaScript files. After those assets load, CSV Guard makes no network requests; disconnect and the cleaner keeps working. Inspect the viewable source if you want to verify the implementation.
Straight answers
FAQ
Does CSV Guard upload my file?
No. File content is parsed and cleaned locally in your browser.
Which delimiters are supported?
Comma, semicolon, tab, and pipe delimiters are detected automatically.
Will it change my original file?
No. Your original remains untouched. CSV Guard downloads a separate .apostrophe-prefixed.csv or .tab-apostrophe-prefixed.csv copy.
Is this a business-rule validation platform?
No. It performs deterministic hygiene checks; it does not decide whether an email, identifier, or address is factually correct.