csv-column-stats

Paste or drop a CSV and instantly see per-column statistics — no upload, no sign-in, all in your browser.

What it does

Give it a CSV by pasting text, dropping a .csv file, or picking one with the file button. It parses the data locally and shows a table with one row per column:

• Numeric columns — min, max, mean, and median.
• Text columns — number of unique values and the most frequent one.
• Every column — how many values are missing (empty or whitespace) and how many are present.

Each column is labelled Numeric or Text so you can see at a glance how it was interpreted. Nothing is sent to a server — parsing and stats run entirely in the page.

Click any column header (or Tab to it and press Enter or Space) to sort the table by that column. Activating the same header again reverses the order; a third activation restores the original CSV column order. Only one column is sorted at a time, missing values always sort to the bottom, and the active header shows an arrow (▲ ascending, ▼ descending) alongside aria-sort for assistive tech.

Getting started

bun install
bun run dev

Open http://localhost:3000 and paste a CSV.

Commands

Command	Does
bun run dev	dev server
bun run build	production build
bun run lint	Biome check
bun run typecheck	route typegen + tsc
bun run test	unit tests (Vitest)
bun run test:e2e	end-to-end tests (Playwright)
bun run test:a11y	accessibility scan (axe-core, WCAG 2.2 AA)

How it works

• lib/parseCsv.ts — wraps Papa Parse (header: true, skipEmptyLines: "greedy"), returning clean Record<string, string> rows plus any parse error.
• lib/stats.ts — pure functions that classify each column and compute its statistics. Fully unit-tested.
• lib/sortStats.ts — the pure three-state sort cycle (ascending → descending → original order) and comparator, including the null-sinks-to-bottom and tie-break-by-name rules. Fully unit-tested.
• components/ — CsvInput (paste / drop / pick), StatsTable, SortableHeader (the clickable, keyboard-operable column header), and TypeBadge, one per file.
• app/page.tsx — wires input to stats and renders the empty, error, and results states.

Testing

Unit tests live beside the code they cover (lib/*.test.ts). End-to-end and accessibility specs live in e2e/. Every route is scanned against WCAG 2.2 A + AA — add new routes to the ROUTES array in e2e/a11y.spec.ts, since an unlisted route is not covered.

Tech stack

Bun, Next.js App Router, TypeScript strict, Tailwind CSS v4, Biome, Vitest, Playwright, Papa Parse.

Deployment

Deployed on Vercel. Every pull request gets a preview build; production deploys are manual.