CSV Cleaver

Splits large CSV files into smaller ones that Excel can open, without damaging them on the way through.

A desktop application for macOS, Windows and Linux, written in Clojure with a cljfx interface. Available in English, Spanish, French, German, Italian, Portuguese, Chinese and Japanese.

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Which document do you want?

If you are…	Read
Someone who needs to split a file	docs/USER-GUIDE.md
A developer changing the code	docs/DEVELOPING.md
Deciding whether a behaviour is a bug	docs/SPECIFICATION.md
Wondering why something was built this way	docs/DECISIONS.md
Driving it from a script	docs/API.md
Assessing the security of any of it	docs/SECURITY.md
Asking who — and what — wrote this	docs/PROVENANCE.md
Checking what is verified, and how	docs/VERIFICATION.md
Turning on signing and notarisation	docs/SIGNING.md

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What it does differently

Most tools that split a CSV file count lines. That is wrong, and quietly so. A CSV value wrapped in quotation marks may contain line breaks, so one row can occupy several lines:

id,notes
1,"first line
second line"

Counting lines cuts that row in half and damages both pieces, without complaint. CSV Cleaver works in whole records, so this cannot happen.

It also:

• Never overwrites anything without asking. The output folder is checked before a single byte is written, and if any file would be replaced you are shown the list and asked.
• Keeps the encoding. UTF-8, UTF-8 with a byte-order mark, or the windows-1252 that Excel writes — whatever went in comes out, mark included, so results open correctly rather than full of mojibake.
• Copies damaged rows untouched. A malformed row is reported, never repaired and never dropped.
• Stays inside Excel's limits. When splitting by size — where you choose megabytes and never a row count — files also stop at 1,048,576 rows, because a file Excel cannot open would defeat the point.
• Can be scripted. An optional local HTTP service, with a Swagger page, puts all of the above behind an API. Off unless you ask for it — see docs/API.md.

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Installing

Download an installer from the releases page. Each one contains its own Java runtime; nothing else is needed.

The installers are not code signed, so each system will warn you the first time. docs/USER-GUIDE.md explains what to click.

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Running from source

Needs JDK 25 and the Clojure CLI. Babashka is recommended but optional.

bb run

Or without Babashka:

clojure -M:run

Command line options:

bb run -- --locale ja --theme dark

Option	Meaning
-l, --locale TAG	Interface language: en, es, fr, de, it, pt, zh, ja. Defaults to the system language, then English.
-t, --theme NAME	auto (follows the system, the default), light or dark.
-h, --help	Show all options.
-V, --version	Show the version.
--api	Start the local HTTP service. Off unless given — see docs/API.md.
--api-port PORT	Port for it. Default 8377.
--api-input MODE	What it accepts: none, path, upload or both. Default path.
--api-token TOKEN	Use a token you already have. One is generated and printed otherwise.
--headless	No window. Only useful with --api.

Scripting it

bb run -- --api --headless

prints a token and a link to a Swagger page at http://127.0.0.1:8377/api-docs/index.html, from which every endpoint can be tried. It listens on this machine only and answers nothing without the token. docs/API.md has the endpoints; docs/SECURITY.md has what it costs — read the part about --api-input path before using it.

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Common tasks

bb tasks

Task	What it does
bb test	The whole test suite
bb coverage	Tests plus a coverage report in target/coverage
bb mutate	Break the code on purpose and check the tests notice
bb lint	clj-kondo
bb format	Reformat with cljfmt
bb check	Everything CI runs
bb shots	Render every screen to target/shots as PNG, both themes
bb icons	Regenerate every platform icon from dev/icons.clj
bb uber	Build the standalone jar
bb package	Build a native installer for this machine
bb brand	Change the name, colour or icons
bb languages	List languages and which have been reviewed

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Provenance

This codebase was written predominantly by Claude (Anthropic) under the direction of Andrew David Nimmo as Technical Project Manager — who set the requirements, made the decisions, and acceptance-tested every build. docs/PROVENANCE.md says precisely what that means, including the copyright position for AI-generated code.

Made with 🤖 in Barcelona.

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Licence

Copyright © 2026 Andrew David Nimmo.

Apache License 2.0 — see LICENSE.

The installers bundle a Java runtime under the GPL v2 with Classpath Exception. See NOTICE and THIRD-PARTY.md.