Format numbers every way
One number, six formats. Thousands separators, scientific & engineering notation, accounting parentheses, and Roman numerals — all updated live.
How to format numbers
Pick decimals, separator, and read every format at once. Click copy beside any row to grab it.
- 01
Type a number
Any finite decimal — negative ok.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
inpututf-8client-sidevalidatedin · textn · set1234567.891
loaded · parsedclient-side - 02
Pick decimals
0 to 10 places. Affects all formats.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
precisionoptionslivememoisedtogglesd · memoised2 · live.89 → .89
options set · memoisedlive - 03
Choose separator
Comma, space, dot (Europe), or none.
Randomness — where used — comes from
crypto.getRandomValues, neverMath.random. Heavy work sits inuseMemo.sepcomputeinstantlocaldeterministicsep · instant, · computed1,234,567.89
computed · instantinstant - 04
Copy a format
One click for each row.
Copy writes through
navigator.clipboardand downloads use aBlob— zero network traffic. Same input plus same options always yield the same bytes.exportcopydownloadzero-networkreproducibleok · copiedready · copiedCopied
shipped · ready to shipsuccess
Pro tips for everyday utilities
Reach for crypto.getRandomValues
Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.
Mock data with seeds
Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.
Reference cards beat memory
Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.
Browser APIs vary
Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.
Persist in the right place
localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.
When format matters
Reports, invoices, science, history.
Reports
Thousands separators for executive summaries. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.
CSPRNG-backedInvoices
Accounting style wraps negatives in parens. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.
reproducibleScience
Scientific notation for very large/small numbers. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.
snappyEngineering
Engineering notation keeps exponent ≡ 0 mod 3. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.
feature-detectedRoman numerals
Movie copyright dates, regnal numbers. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.
deterministici18n
Switch separators for European audiences. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.
production-readyFrequently asked questions
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