Developer Utilities
Small developer utilities that save a trip to a random website. Encode and decode Base64, explain a regex, build UTM links, generate QR codes and vCards, and more — the everyday helpers. Free in your browser, and available by API when you need them in a script.
Developer Utilities
Work of gas expansion calculator
W = −P_ext·ΔV, free
POST /chem/work-gas-expansion$0.002Developer Utilities
Zero-order half-life calculator
t½ = [A]₀/(2k), free
POST /chem/zero-order-half-life$0.002Developer Utilities
WCAG contrast ratio checker
AA/AAA for normal and large text
POST /color/contrast$0.002Developer Utilities
RGB to hex converter
0–255 channels to #RRGGBB, free
POST /color/rgb-hex$0.002Developer Utilities
RGB to HSV converter
0–255 channels to hue, saturation, value, free
POST /color/rgb-hsv$0.002Developer Utilities
RGB to LAB converter
sRGB channels to CIE L*a*b* (D65), free
POST /color/rgb-lab$0.002Developer Utilities
Color temperature to RGB
Kelvin 1000–40000 to sRGB, free
POST /color/temperature$0.002Developer Utilities
Tetradic color scheme generator
four hues from one hex, free
POST /color/tetradic$0.002Developer Utilities
Combinations with repetition
multiset C(n+r−1, r), free
POST /combo/combinations-with-repetition$0.002Developer Utilities
Handshake problem calculator
n choose 2 and inverse, free
POST /combo/handshake$0.002Developer Utilities
Monotone lattice paths on an a×b grid
C(a+b, a), free
POST /combo/lattice-paths$0.002Developer Utilities
Unsigned Stirling numbers of the first kind
c(n,k) cycles, free
POST /combo/stirling-first$0.002Developer Utilities
Butter measurement converter
sticks, tbsp, cups, grams free
POST /cook/butter$0.002Developer Utilities
Cake tin size converter
round ↔ square by area, in & cm free
POST /cook/cake-tin$0.002Developer Utilities
Honey cups to grams converter
tbsp & density free
POST /cook/honey$0.002Developer Utilities
Pints to liters converter
US & imperial pint free
POST /cook/pints-liters$0.002Developer Utilities
Teaspoons to ml converter
US & metric tsp free
POST /cook/tsp-ml$0.002Developer Utilities
Add months to a date
shift calendar date with month-end clamp, free
POST /date/add-months$0.002Developer Utilities
Birthstone by birth month
traditional and modern stones, free
POST /date/birthstone$0.002Developer Utilities
Chinese zodiac sign calculator
animal by year and lunar New Year, free
POST /date/chinese-zodiac$0.002Developer Utilities
Days between two dates
whole calendar day count, free
POST /date/days-between$0.002Developer Utilities
Days elapsed in the year
days since January 1, free
POST /date/days-elapsed-year$0.002Developer Utilities
Easter Sunday date calculator
Gregorian computus by year, free
POST /date/easter-sunday$0.002Developer Utilities
Julian Day to date converter
Gregorian calendar from JDN, free
POST /date/from-julian-day$0.002Developer Utilities
Golden number and epact calculator
ecclesiastical year numbers, free
POST /date/golden-number$0.002Developer Utilities
ISO week number calculator
week and week-year from any date, free
POST /date/iso-week-number$0.002Developer Utilities
ISO week to date converter
calendar date from week year, free
POST /date/iso-week-to-date$0.002Developer Utilities
First and last day of month
calendar start and end dates, free
POST /date/month-start-end$0.002Developer Utilities
Next leap year finder
next Gregorian leap year on or after a year, free
POST /date/next-leap-year$0.002Developer Utilities
Next occurrence of a weekday
next Monday/Friday date from any day, free
POST /date/next-weekday$0.002Developer Utilities
Subtract days from a date
earlier calendar date calculator, free
POST /date/subtract-days$0.002Developer Utilities
Antenna length calculator
quarter-wave and half-wave from frequency, free
POST /elec/antenna-length$0.002Developer Utilities
Battery runtime calculator
hours from Wh and load watts, free
POST /elec/battery-runtime-wh$0.002Developer Utilities
Capacitor energy calculator
E = ½CV² in joules, free
POST /elec/capacitor-energy$0.002Developer Utilities
Speaker crossover calculator
frequency from L and C, free
POST /elec/crossover-frequency$0.002Developer Utilities
dBm to dBW calculator
convert dBm to dBW, free
POST /elec/dbm-to-dbw$0.002Developer Utilities
dBm to watts calculator
convert dBm to W and mW, free
POST /elec/dbm-to-watts$0.002Developer Utilities
Electric potential calculator
V=kQ/r for a point charge, free
POST /elec/electric-potential$0.002Developer Utilities
EMF terminal voltage calculator
V = ε − Ir free
POST /elec/emf-internal-resistance$0.002Developer Utilities
Inductor energy calculator
E = ½LI² in joules, free
POST /elec/inductor-energy$0.002Developer Utilities
kWh calculator
energy from watts and running time, free
POST /elec/kwh-calculator$0.002Developer Utilities
Inverting amplifier calculator
op-amp gain Av = −Rf/Rin, free
POST /elec/op-amp-inverting$0.002Developer Utilities
Electrical power calculator
P=VI and P=I²R from any two values, free
POST /elec/power-vi$0.002Developer Utilities
Parallel resistance calculator
equivalent Req from R1∥R2∥…, free
POST /elec/resistors-parallel$0.002Developer Utilities
RLC resonant frequency calculator
f₀ and Q from L, C, R, free
POST /elec/rlc-resonance$0.002Developer Utilities
Smoothing capacitor calculator
C = I/(2f·Vr) filter size, free
POST /elec/smoothing-capacitor$0.002Developer Utilities
Solenoid magnetic field calculator
B = μ₀ n I, free
POST /elec/solenoid-field$0.002Developer Utilities
Baconian cipher encoder and decoder
five-letter A/B codes, free
POST /enc/bacon$0.002Developer Utilities
Base45 encoder and decoder
RFC 9285 for QR credentials, free
POST /enc/base45$0.002Developer Utilities
Base64url encoder and decoder
URL-safe, no padding, free
POST /enc/base64url$0.002Developer Utilities
Columnar transposition cipher
encrypt decrypt with keyword, free
POST /enc/columnar$0.002Developer Utilities
Text to ASCII codes converter
decimal char codes, free
POST /enc/decimal-ascii$0.002Developer Utilities
Four-square cipher encoder and decoder
two keywords, free
POST /enc/four-square$0.002Developer Utilities
HTML entities encoder and decoder
named and numeric, free
POST /enc/html-entities$0.002Developer Utilities
Morse code translator
encode and decode text free
POST /enc/morse$0.002Developer Utilities
Quoted-printable encoder and decoder
MIME QP encode/decode, free
POST /enc/quoted-printable$0.002Developer Utilities
ROT47 encoder and decoder
printable ASCII cipher, free
POST /enc/rot47$0.002Developer Utilities
Flag semaphore translator
encode and decode arm positions free
POST /enc/semaphore$0.002Developer Utilities
Trithemius cipher encoder and decoder
progressive shift, free
POST /enc/trithemius$0.002Developer Utilities
Vigenère cipher encoder and decoder
keyword polyalphabetic, free
POST /enc/vigenere$0.002