Number Expression

Every ComfyUI user eventually needs to do math that the primitive math nodes can't express in one step. Number Expression is the node that lets you write (a * b) / 2 + c instead of chaining three Math nodes and squinting at the wires. You type a formula, it evaluates it, and the answer leaves as a NUMBER, a FLOAT, an INT, a BOOLEAN and text all at once.

It's the middle ground between ComfyUI's fiddly single-operation math nodes and the "power user runs a Python node" approach. The nice bit is the sandboxing: this is not a general-purpose code runner. Only arithmetic reads - the allowed function list is short and named, and anything else is refused by name before it runs. If you've ever pasted a workflow containing a PythonScript node you didn't fully trust, you can see why that's a feature.

The expression language

Slots a through x give you 24 numbers, each typed in or wired from elsewhere. A slot the expression never mentions is simply ignored; unconnected slots use their widget value. Then the expression box is your formula:

(a * b) / 2 + c
clamp(a, 0, 1)
round(a / b, 2)
a if a > b else b

Functions available: min, max, abs, round, floor, ceil, sqrt, clamp(v, lo, hi), lerp(a, b, t), sign, log, log2, log10, exp, sin, cos, tan, atan2, hypot, degrees, radians. Constants pi, e and tau are there, comparisons work, and and/or combine conditions. The expression box takes several lines joined into one, and # starts a comment.

The boolean output deserves a mention: a > b answers 1 or 0 on the number outputs, but the BOOLEAN socket carries the real true/false - wire that into a switch and you've built a comparison node too.

Outputs, and one honest caveat

• number - the answer on the NUMBER wire, whole where it came out whole.
• float / int - the same answer as a decimal and as an integer (int cuts the fraction off rather than rounding, so 3.9 leaves as 3).
• boolean - false when the answer is 0, true otherwise.
• text - the answer written out (4.5 or 7), which is what you feed into a filename prefix or a text join.

Watch the int behavior: round(3.7) gives 4.0 on the float side but 3 on the int side because int truncates. Use round() if you actually want rounding - the tooltips make the distinction explicit and it's a real trap.

Setup and gotchas

decimals sets how many places a fractional answer is rounded to (6 = 0.333333, 2 = 0.33, 0 = whole). on_error decides what happens when the expression is refused or impossible: error stops the run and names the cause; zero logs it and answers 0. The one genuinely foot-gun case is a / b with b at 0 - that stops the run unless on_error is zero.

This node ships in WAS Node Suite v3 - install via ComfyUI Manager (search WAS Node Suite v3) or:

cd ComfyUI/custom_nodes
git clone https://github.com/WASasquatch/was-node-suite-comfyui

Restart after cloning; you need ComfyUI 0.14.0+ and Python 3.10+. No extra packages - v3's rewrite deliberately dropped the pack's old twenty-dependency install, and nothing gets downloaded on startup.

Honestly, the use case that keeps this node on my canvas is filenames and captions. Build a frame number or a scaled value, push the text output into a save prefix, and every render names itself correctly.