CSV vs XLSX for Lead Lists: Which to Use and When
Most lead tools offer both, most people pick whichever is first in the dropdown, and then spend twenty minutes wondering why the phone numbers look wrong.
The two formats fail in completely different places. Knowing which one you're handing to which system removes an entire category of annoyance.
What CSV Actually Is
A CSV is a text file. Rows separated by newlines, fields separated by commas, and nothing else. There is no concept of a cell type, a column width, a formula, or a second sheet. It is the plainest possible way to move a table between two systems.
That plainness is exactly why it's the default for data interchange. Every CRM, database, and scripting language reads CSV without a library. It's small, diffable, and there is no version of it that one tool understands and another doesn't.
Where CSV Falls Down
Because a CSV carries no type information, the program opening it has to guess — and Excel guesses badly.
A UK phone number like 0113 249 6000 looks numeric, so Excel strips the leading zero. A postcode fragment can be read as a date. A long company registration number becomes scientific notation. None of this is recoverable once the file has been opened and saved; the original data is simply gone.
Encoding is the other problem. A CSV has no header declaring its character set, so Excel on Windows assumes Windows-1252 unless the file opens with a byte order mark. Pound signs and accented characters mangle. Both of these are covered in more detail in the clean CSV export checklist, along with the fixes.
There's also the comma itself. Business names contain commas — "Smith, Jones & Partners" — which means quoting, and quoting means escaping quotes inside quoted fields. Well-built exporters handle this correctly. Hand-rolled ones frequently don't, and you discover it when one row has shunted three columns to the right.
What XLSX Gives You
XLSX is a real spreadsheet format. Cells carry types, so a phone number stored as text stays text, a date stays a date, and nothing is inferred at open time. Encoding is stored internally, so there is no mojibake and no byte order mark question.
You also get things a CSV structurally cannot hold: multiple sheets, column widths, frozen headers, and formatting. For a lead list you're handing to a colleague or a client, that matters more than it sounds — a file that opens with readable column widths and a frozen header row gets used, and a wall of unformatted text gets ignored.
Where XLSX Falls Down
It's a zipped XML bundle, which makes it opaque. You can't grep it, diff it, or eyeball it in a text editor. If something is wrong you need a spreadsheet application to find out what.
Some older or simpler CRM importers accept CSV only. Scripts need a library to read it. And at very large row counts it's heavier to parse than the equivalent CSV, though for anything under a few hundred thousand rows this is theoretical.
The Practical Rule
Use XLSX when a human is going to open the file. Use CSV when a machine is going to read it.
If you're sending a list to a colleague, a client, or a VA who'll work through it in Excel, send XLSX. The leading zeros survive, the pound signs survive, and it opens looking like something a person made.
If you're importing into HubSpot, Pipedrive, or anything with a CSV importer, send CSV — but format the fields properly first. Phone numbers in E.164, a consistent empty-cell convention, tracking parameters stripped from URLs. Get that right and the CSV's lack of typing stops mattering, because there's nothing left for the importer to guess about. The UK phone formatting guide covers the field that breaks most often.
A Note on Google Sheets
Google Sheets handles UTF-8 correctly on import without a byte order mark, which removes the encoding half of the problem. It does not remove the type-inference half — it will still eat a leading zero unless the value starts with a plus or you set the column format before pasting.
If you're working in Sheets, import via File then Import rather than pasting, and you'll get an options dialog that lets you disable automatic type conversion. Pasting gives you no such control.
Getting Either One Cleanly
LeadSnipe exports both, and applies the same formatting pipeline to each: UK phones to E.164, tracking parameters stripped, name junk trimmed, a consistent empty-cell rule, and non-destructive deduplication. The CSV is UTF-8 and the XLSX is properly typed, so whichever you pick, the data arrives intact. If you're deciding where the list should live afterwards, spreadsheet or CRM covers that, and the HubSpot import guide covers the mapping step.