How does it know which base I typed?

If you prefix the number it auto-detects: 0x for hexadecimal, 0b for binary, 0o for octal, and a plain number is treated as decimal. You can also force a base with the selector. It converts the value into all four bases at once so you can read it however you need.

Does it handle very large numbers?

Yes. It uses JavaScript BigInt internally, so it is exact for integers of any size - well past the 2^53 limit where normal floating-point numbers start losing precision. That matters for things like 64-bit IDs, bitmasks, and hashes.

Can I use it for file permissions or bitmasks?

Yes - this is the everyday backend use. chmod permissions are octal (0o755), color and byte values are hex, and feature flags and permission sets are bitmasks you read in binary. Seeing the same value in all four bases at once makes those much easier to reason about.

Free tool · Runs in your browser

Number base converter.

Type a number and see it in hex, decimal, binary, and octal at once — auto-detecting 0x, 0b, and 0o prefixes, with arbitrary-size integers (BigInt) for 64-bit IDs and bitmasks.

One value, four ways to read it

Backend work is full of the same number wearing different bases: file permissions in octal, byte and color values in hex, feature flags and permission sets as binary bitmasks, IDs in decimal. Converting in your head is error-prone, and normal JavaScript silently loses precision past 2^53 — right where 64-bit identifiers live. This shows every base at once and stays exact at any size, so you can read a value however the system in front of you expects it.

Related free tools

Epoch / timestamp converterUnix timestamp both ways UUID generatorRandom v4 UUIDs Hash generatorSHA-256/512 of text Base64 encode / decodeEncode/decode Base64

All free tools →

Free tools for the backend you run.

One of a set of free developer tools from Infraveil — the control plane for running, securing, and watching your backend on servers you own. Browse the rest, no signup.

See all free tools

Get the backend toolkit

Practical tools and guides for shipping and running a backend you own. No spam.