Numderline is a font patcher that uses OpenType font shaping trickery to make it easier to visually parse large numbers. It has multiple variants for different preferences, fonts and contexts.

I (Tristan Hume) was inspired to build this by my job at Jane Street involving staring at a lot of large numbers, mostly latencies in nanoseconds, and wanting to pick out larger quantities like milliseconds and microseconds.

See the code on Github to contribute or patch fonts of your choice.


The flagship "Numderline" variant underlines alternating groups of 3 digits. It's what I use at work.

Download (hover to view): DejaVuSansMono UbuntuMono DroidMono Cousine SauceCode Lekton


This variant squishes digits together into groups of 3. It's nice looking and works for most fonts but is annoying for editable text since it jumps around while typing.

Download (hover to view): DejaVuSansMono UbuntuMono Hack SauceCode


For fonts with lots of weights, making alternating groups slightly bolder is an alternative to underlines.

Download (hover to view): SauceCode


Inserting fake commas is a good option in proportional contexts where changing the width doesn't matter.

Download (hover to view): DejaVuSans

Monospace Commas

By combining the grouping variant with tiny commas this variant adds commas while remaining monospaced.

Download (hover to view): DejaVuSansMono UbuntuMono Hack SauceCode


The debug version shows how the font uses shaping tricks to replace digits with alternate versions that track the position modulo 7.

Download (hover to view): DejaVuSansMono