Guides &amp; tutorials for generating and validating data

UUID v4 vs v7: random IDs versus time-ordered keys

v4 hides time. v7 keeps your B-tree sane. Same hyphenated string, different index behavior.

Randomly 8 min

Product

A game-night pack: dice, trivia, and a movie when nobody wants to pick

The silly tools are still tools. How I use the roller, trivia, and a random movie without turning the evening into a product demo.

Text

Humanize text: stripping the tells I keep seeing in model output

Em dashes, “delve,” neat little lists. A local cleaner for the patterns that make prose look generated.

Names

Sampling baby names without pretending the SSA list is the world

US Social Security files are a specific dataset. Random names from them are useful, and they are biased.

Math

Fair dice in a browser: modulo bias and why I care on a d20

Math.random() is not a tabletop argument. Rejection sampling is. How the roller keeps faces honest.

Design

HEX, RGB, and HSL: three ways to say the same color

Design tools hop formats. Rounding errors hop with them. A small translation guide plus a palette generator.

Math

Fibonacci with BigInt: when F(n) no longer fits in a number

JavaScript Number dies around F(78). The sequence does not. Here is how the tool keeps going.

MAC addresses and OUI prefixes for network tests

Six bytes, a vendor prefix, a locally administered bit. How to mint addresses that look plugged in.

Validators

VAT format vs VIES: checksums are not registration

A number can look like a VAT ID and still be unregistered. Format first, then the official lookup if you must.

Product

How Randomly datasets get from public sources into a small sample

R2 shards, D1 catalogs, and why your browser does not download GeoNames in one gulp.

Validators

SSN format checks are not identity checks

Area, group, serial. Invalid ranges. Why a green validator still must never mean “this person exists.”

Dates

Unix time: seconds, milliseconds, and the 2038 hangover

A timestamp is an integer. The unit is the part everyone forgets until the date lands in 1970 or 5138.

Hashes and encoding

Base64 is encoding, not encryption

If you can reverse it without a key, you did not encrypt anything. Base64 is for bytes in text. That is all.

Test Data

PII-safe test data: fixtures that do not leak real people

The fastest way to fail a security review is a production dump in staging. Build synthetic people instead.

ABA routing numbers: the 3-7-1 checksum banks still use

Nine digits, a weighted sum, mod 10. How to generate format-valid routing numbers for ACH fixtures.

VIN check digits and what NHTSA actually returns

ISO 3779 stamps one check character. Decoding a real vehicle is a different call, to a government API.

Hashes and encoding

MD5 vs SHA-256: checksums, collisions, and what browsers still compute

MD5 is fine for catching a botched download. It is not a password hash. SHA-256 is the workhorse I reach for instead.

Test Data

Luhn test cards: valid checksums that must never charge

The Luhn digit is a filter for typos, not a payment. How to mint test PANs and keep them out of production.

Generators

Passwords vs passphrases: entropy you can still type

A 16-character random password and a four-word phrase can land in the same entropy band. The typing story is not the same.

IBAN check digits: how mod-97 actually works

Two digits near the front of an IBAN are the whole checksum. Here is the rearrange-and-remainder procedure, and why BigInt matters.