Sound level at another distance (inverse-square law; line sources fall 3 dB per doubling), or the distance for a level.

Weekday of any date from year 1 to 9999 (Gregorian or Julian calendar) with day of year, quarter, ISO week and ISO week-date.

Frequencies, cents and ratios of the 12 notes in equal, 5-limit just, Pythagorean or quarter-comma meantone tuning.

Moon phase name, age in days, approximate illumination and the previous/next new, quarter and full moon times for a date.

Julian Day, modified JD and Julian Day Number for a date and UTC time (Gregorian or Julian calendar), or JD back to a date.

Convert between Gregorian and Julian calendar dates (Old Style / New Style) with the day difference for that date.

Convert a Gregorian date to the Hebrew calendar (or back) with leap year, year type and major holiday dates.

Chinese zodiac animal, element, yin/yang and Chinese New Year date for a year or a date (New Year table 1901-2100).

Age in years, months, days and days lived, Korean and East Asian ages, next birthday with leap-day rules, and zodiac.

Room mode frequencies (axial, tangential, oblique) for a rectangular room, plus Schroeder frequency from RT60.

Classify an IPv4 or IPv6 address: public, private, loopback, link-local, CGNAT or reserved, plus reverse-DNS name.

Compare two semver versions by precedence and test whether a version satisfies a range like ^1.2.0 or >=2 <3.

SHA-256, SHA-1, SHA-512 and MD5 digests of a short text in hex and base64, with byte length and base64 encoding.

Explain a 5-field cron expression in plain English and list the next 5 run times in UTC.

Check email address syntax, role accounts (info@, admin@) and known throwaway domains. No DNS lookup, nothing sent.

Text statistics for English: words, sentences, reading time and Flesch reading ease with a difficulty verdict.

Normalize a URL: lowercase host, default port and fragment removed, sorted query, tracking parameters stripped.

Repair broken JSON: trailing commas, single quotes, bare keys, comments, Python None/True, missing brackets. Returns parsed.

Convert a unix timestamp or ISO time to ISO, local time in any IANA zone, weekday, ISO week and relative time.

Structural diff of two JSON documents: added, removed, changed and type-changed paths, arrays compared by index.