Tools starting with R

Pick fairly from a list, generate random numbers, or shuffle items into a random order.

Generate cryptographically random tokens with a chosen alphabet, and see their entropy.

Simplify a ratio, scale it up, or solve for a missing value.

Produce a receipt confirming a payment, with items, tax and the amount paid.

Work out how much food to cook for a number of people, by course and appetite.

Scale a recipe up or down by servings, rewriting every quantity as a fraction a kitchen can measure.

Escape text so it is treated as a literal inside a regular expression.

Break a regular expression into pieces and explain what each one does in plain English.

Build a regular expression from tested patterns, with anchors and flags, and try it against sample text.

Pull every match out of text, with capture groups, named groups and positions.

Test a regular expression replacement with capture groups and see the result live.

Split text on a regular expression and see each resulting part, empties included.

Test a regular expression against sample text with live highlighting and capture groups.

Remove repeated lines from a list, with options to sort, trim whitespace and ignore case.

Strip EXIF, GPS and camera data from a photo, then verify the result is clean.

Rearrange, reverse or remove PDF pages with thumbnails to see what you are moving.

Read a resistor's value from its colour bands, with tolerance and the range it may fall in.

Change every page to A4, Letter or another standard size, scaling content to fit.

Find the pixel dimensions and megapixels needed to print at a given size and resolution.

Project a retirement pot from monthly contributions, and what it might pay out.

Reverse text by character, word or line — including emoji and accents, handled correctly.

Convert RGB to CMYK percentages, with hex, HSL and HSV alongside.

Convert RGB values to HSL, plus hex, HSV and CMYK, with a live swatch.

Convert RGB to HSV/HSB, the model behind most colour pickers.

Build a robots.txt file, including an optional opt-out for AI training crawlers.

Test whether a URL is allowed for a given crawler, and check a robots.txt for mistakes.

Calculate return on investment as a percentage, plus annualised return over a holding period.

Work out roof area from the footprint and pitch, in squares and bundles, with a waste allowance.

Calculate a room's floor area, wall area and volume in metric and imperial units.

Rotate an image in 90° steps and flip it horizontally or vertically.

Round an image's corners, with the removed areas genuinely transparent.

Keep only the CSV rows matching a condition on one column.

Convert between spindle RPM, cutting speed, surface speed and pulley ratios.

Generate an RSA key pair in the browser and export it as PEM or JWK, for signing or encryption.

Work out pace, finish time or distance for a run, with splits for common races.