LeadSlicer — Split and Clean CSV Files Offline

Anyone who has worked in a sales or dispatch office knows this job. A 50,000-row lead list arrives. It needs the duplicates removed, the empty rows stripped, three columns kept out of nineteen, and then it has to be cut into 500-row chunks — one per agent.

The usual options are all bad. Excel struggles and mangles your phone numbers into scientific notation. An online splitter wants you to upload a file full of customer phone numbers to a site with no name on it. A Python script works, but the person who actually needs this doesn't have Python.

LeadSlicer is the fourth option: free, offline, browser-based. Your files never leave your device.

The seven-step flow

1. Upload — drag & drop any .csv, .xlsx or .xls file
2. Preview — first rows, total row and column counts
3. Configure headers — use the first row, or auto-generate column names
4. Select columns — keep only the fields you need
5. Filter & clean — remove duplicates, empty rows and rows with missing values
6. Chunk — split into files of any size: 100, 500, 1000+ rows
7. Download — individual files, or everything as one ZIP

Each chunk can be previewed before you download it, because finding out the split was wrong after you've emailed eight agents is how the afternoon disappears.

Formats come out the way they went in

This is the detail that decides whether a tool like this is usable. Dates, currency and number formats are preserved exactly. No +923001234567 turning into 9.23E+11, no leading zeros eaten, no 03/04 silently becoming April 3rd.

Deduplication runs on any column you choose — Email, Phone, Company — not on whole-row equality, because two records for the same person are almost never byte-identical.

Why in-browser is the right call here

Three reasons, in the order that actually matters to a sales office:

Privacy. Lead files are customer data. In most companies, uploading them to an unvetted website is a policy breach even when nobody notices. A tool that runs locally sidesteps the entire conversation.

No install. It's a web page. The agent who needs it opens a link. There's no IT ticket, no admin password, no Python.

Offline. It's an installable PWA, so once loaded it works with no internet at all — on Android, iOS or desktop. Handy when the office Wi-Fi is the bottleneck.

Details that make it pleasant

• Light / dark / system themes with six accent colours
• Keyboard navigable, semantic HTML — it works with a screen reader
• Responsive down to a phone, because half the people using it are on one
• ZIP download so you get one file instead of forty

None of that is clever engineering. It's the difference between a tool people use twice and a tool people keep in their bookmarks bar.

The same pattern, again

LeadSlicer is the third tool I've built on the same idea as ToolForge and CV Studio: take a job that everyone assumes needs a server, and notice that the browser has been able to do it for years.

Parsing spreadsheets, hashing, zipping, rendering PDFs, reading the camera — all local APIs now. Most "upload your file here" products are charging for a round trip that doesn't need to happen.

Try it

Online: leadslicer.abdulmanan.tech — no install, no account.

Locally:

git clone https://github.com/abdulmanan69/leadslicer.git
cd leadslicer
# open index.html — that's the whole setup

MIT licensed, source on GitHub. If your team has a file-wrangling job that eats an afternoon every week, tell me about it — those are my favourite things to build.