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No-bullshit password validator using raw entropy values. Hit the project with a star if you find it useful

Supported by Qvault


This project can be used to front a password strength meter, or simply validate password strength on the server. Benefits:

  • No stupid rules (doesn't require uppercase, numbers, special characters, etc)
  • Everything is based on entropy (raw cryptographic strength of the password)
  • Inspired by this XKCD

XKCD Passwords

⚙️ Installation

Outside of a Go module:

go get

🚀 Quick Start

package main

import (
    passwordvalidator ""

func main(){
    entropy := passwordvalidator.GetEntropy("a longer password")
    // entropy is a float64, representing the strength in base 2 (bits)

    const minEntropyBits = 60
    err := passwordvalidator.Validate("some password", minEntropyBits)
    // if the password has enough entropy, err is nil
    // otherwise, a formatted error message is provided explaining
    // how to increase the strength of the password
    // (safe to show to the client)

What Entropy Value Should I Use?

It's up to you. That said, here is a pretty good graph that shows some timings for different values:


Somewhere in the 50-70 range seems "average"

How It Works

First, we determine the "base" number. The base is a sum of the different "character sets" found in the password.

The current character sets include:

  • 26 lowercase letters
  • 26 uppercase
  • 10 digits
  • 32 special characters - !"#$%&'()*+,-./:;<=>?@[\]^_{|}~

Using at least one character from each set your base number will be 94: 26+26+10+32 = 94

Every unique character that doesn't match one of those sets will add 1 to the base.

If you only use, for example, lowercase letters and numbers, your base will be 36: 26+10 = 36.

After we have calculated a base, the total number of brute-force-guesses is found using the following formulae: base^length

A password using base 26 with 7 characters would require 26^7, or 8031810176 guesses.

Once we know the number of guesses it would take, we can calculate the actual entropy in bits using log2(guesses)

The calculations are done in log space in practice to avoid numeric overflow.

Additional Safety

To add further safety to dumb passwords like aaaaaaaaaaaaa, or 123123123, We modify the length of the password to count any more than two of the same character as 0.

  • aaaa has length 2
  • 12121234 has length 6

💬 Contact

Twitter Follow

Submit an issue (above in the issues tab)

Transient Dependencies

None! And it will stay that way, except of course for the standard library.

👏 Contributing

I love help! Contribute by forking the repo and opening pull requests. Please ensure that your code passes the existing tests and linting, and write tests to test your changes if applicable.

All pull requests should be submitted to the main branch.

go test
go fmt
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