Free CSV Tools
Every free CSV tool CSVUndo offers — one that diagnoses and fixes everything at once, one that compares two files, and a set that repair broken numbers, zeros, characters and dates, or convert, clean, merge, split and join files. Every one runs entirely in your browser: your file is never uploaded, stored, or seen by anyone (verify that yourself in 30 seconds), and each tool keeps working offline once the page has loaded.
All tools
🩺 CSV Doctor
Not sure what’s wrong, or how many things are wrong? Run every check in one pass — scientific notation, stripped zeros, mojibake, ambiguous dates, ragged rows, duplicates — then select and apply the safe fixes right here.
Open the tool →🔍 CSV Compare
See exactly what changed between two CSVs — added, removed and changed rows, matched by position or by a key column like SKU or ID. Duplicate keys are flagged, never guessed at.
Open the tool →🔢 Fix scientific notation
Excel collapsed a UPC, EAN or account number into 8.85909E+11? Expand every value back to its full digit string using exact string math — no floating-point rounding, no precision loss.
0️⃣ Restore leading zeros
ZIP code 00501 became 501, or product code 0071589 lost its zero? Pick the column and the target width and the zeros come back across the whole file in one click.
🔤 Fix broken characters
café instead of café, “ instead of quotes? Reverse the encoding mistake (mojibake) automatically — even in files that were mis-encoded twice.
🛍️ Fix a Shopify product CSV
Shopify import failing, or barcodes, SKUs and titles arriving broken? Repairs all three Excel-caused problems at once — scientific-notation barcodes, dropped SKU zeros and garbled titles — ready to re-import.
Open the tool →🔄 CSV ⇆ TSV converter
Turn a comma file into tab-separated, or switch to semicolons or pipes for a fussy importer. Auto-detects the input delimiter, previews the table, and protects codes on the way out.
Open the tool →🧹 Clean a CSV
Remove duplicate rows, drop blank rows, trim stray spaces, and delete empty columns — in one pass, with a before/after preview. Your header stays put and nothing is uploaded.
Open the tool →🔎 Check CSV encoding
Drop a file and get a plain-English report: UTF-8, UTF-8 with BOM, UTF-16 or legacy ANSI — plus a mojibake warning and the matching fix. Reads the bytes locally; nothing is uploaded.
Open the tool →🔗 Merge CSV files
Combine several CSVs into one — monthly exports into a yearly file — stacked and aligned by column name, with an optional source-file column. Drop them all in; nothing is uploaded.
Open the tool →✂️ Split a large CSV
Too big for Excel to open (past 1,048,576 rows), or need it in chunks? Split by row count or into a set number of files, header repeated in each, download all as a zip. Nothing uploaded.
Open the tool →🔗 Join CSVs by a column
Match two files on a shared key column — a customer list to its orders by ID — the VLOOKUP job without the formula. Left or inner join, in your browser.
Open the tool →📅 Fix date formats
A US machine read 04/11/2023 as 11 April and saved? Convert whole date columns between DD/MM, MM/DD and ISO — you state the source order, and nothing ambiguous is ever guessed.
✅ Validate a CSV
Will an importer reject this file? Checks delimiter, unbalanced quotes, ragged rows (wrong column count), duplicate headers and blank lines against RFC 4180. Nothing is ever flagged by shape alone.
Open the tool →Which tool do I need?
Match the symptom in your file to the tool that fixes it:
| What you see in the file | Tool |
|---|---|
| Not sure what’s wrong, or how many things are wrong | CSV Doctor |
| Need to know what changed between two versions of a file | CSV Compare |
Numbers like 1.23E+12 where barcodes or IDs should be | Fix scientific notation |
| ZIP codes or SKUs missing their leading zeros | Restore leading zeros |
Accents shown as é, †or  | Fix broken characters |
| Right format, wrong delimiter (need tabs, semicolons or pipes) | CSV ⇆ TSV converter |
| Duplicate rows, blank rows, or stray spaces cluttering the file | CSV cleaner |
| Not sure if the file is UTF-8, has a BOM, or is ANSI | CSV encoding checker |
| Several CSVs to combine into one file | Merge CSV files |
| A file too big to open in Excel | Split a large CSV |
| Two files to match up by a shared ID / key column | Join CSVs by column |
| A Shopify import that fails, or barcodes/SKUs/titles broken after Excel | Fix a Shopify CSV |
| Dates flipped DD/MM ⇆ MM/DD after Excel, or mixed formats in one column | Fix date formats |
| Not sure if an importer will reject the file — ragged rows, duplicate headers, bad quotes | CSV validator |
| Every field crammed into one column, or a comma splitting a field | See the guides |
Want the background on why any of this happens and how to prevent it? Every problem has a full write-up in our CSV repair guides.
Comparing tools before you pay? See how we stack up as a free CSVFix alternative — no 50 KB limit and nothing uploaded.
The upload failed — which platform?
Sometimes you don’t know what’s wrong with the file, only that a platform refused it. These decoders start from the error message and work backwards to the cell that caused it:
| Where the import failed | Guide |
|---|---|
| Shopify — “invalid CSV header”, variant conflicts, broken barcodes | Shopify CSV import errors |
| Amazon Seller Central — flat file rejected, valid UPC called invalid | Amazon flat file upload errors |
| eBay File Exchange or Seller Hub — CSV rejected, UPC read as 8.85E+11 | eBay CSV upload errors |
| Etsy — garbled special characters in titles/tags, or SKU zeros stripped | Etsy CSV import errors |
| BigCommerce — product import fails with invalid or duplicate SKU | BigCommerce CSV import errors |
| Google Merchant Center — invalid GTIN or feed encoding rejected | Google Merchant Center feed errors |
| QuickBooks — bank CSV won’t import, date or amount rejected | QuickBooks bank CSV import |
| Mailchimp — contacts rejected, names or phone numbers mangled | Mailchimp contact CSV errors |
| Salesforce Data Loader — “invalid CSV format”, UTF-8 complaints | Salesforce Data Loader errors |
| WooCommerce — the product importer maps columns to nothing | WooCommerce CSV import errors |
| Outlook or Google Contacts — every accented name arrived garbled | Garbled contacts CSV |
| The file is simply too large — Excel truncated it or won’t open it | CSV too big for Excel |
How CSVUndo compares to other CSV tools
When selecting a CSV repair or conversion tool, data privacy, file limits, and specific bug fixes are the most critical factors. Here is how CSVUndo compares to cloud-based converters and general offline utilities:
| Feature / Guarantee | Cloud Converters (e.g. ConvertCSV, CSVFix) | General Offline Tools (e.g. csv.repair) | CSVUndo.com |
|---|---|---|---|
| Data Privacy | Uploads files to remote servers | Local browser processing | 100% Client-Side with connect-src 'none' CSP |
| Cost & File Limits | Free tier capped (e.g. 50 KB size limit) | Free | 100% Free, no paid size gate or account required |
| Excel Corruption Fixers | Generic parsing & conversion | General cleaning & duplicate removal | Dedicated tools for 1.23E+11, lost zeros, & Mojibake |
| Platform Error Workflows | None | None | Pre-configured fixes for Shopify, Amazon, QuickBooks & more |
| Offline Verification | Requires constant internet connection | Works offline | Auditable via DevTools Network tab & works in airplane mode |
Free broken-CSV sample files
Want to see a tool work before trusting it with your own data? Download one of these tiny, deliberately-broken files and drop it into the matching tool. They’re safe, made-up data — no real people or products — so reuse them freely for testing or teaching.
- sample-scientific-notation.csv — UPCs collapsed to
8.85909E+11→ fix it - sample-leading-zeros.csv — ZIP and ID codes missing their zeros → fix it
- sample-mojibake.csv — names full of
JoséandZürich→ fix it - sample-dates.csv — ambiguous
DD/MMdates → fix it or read the guide - sample-tab-separated.tsv — a tab-separated file → convert it
- sample-duplicate-rows.csv — duplicate and blank rows → clean it