Password Entropy

Calculate the entropy, strength rating, and estimated offline crack time of a password. Password is sent over HTTPS and is not stored or logged.

⚡ 1 credit per call

Try it

Fill in the fields below and hit Send.

Why use this

LLMs give inconsistent or wrong answers when asked to evaluate password strength. Use this for accurate entropy calculations based on character set composition and length.

Input

Field	Type	Required	Description
`password`	string	✓	The password to evaluate (1–512 characters)

Response

Field	Values	Description
`length`	number	Number of characters in the password
`charset_size`	number	Size of the detected character set
`charset`	object	Which character classes are present (lowercase, uppercase, digits, symbols)
`entropy_bits`	number	Shannon entropy in bits
`strength`	`very_weak` \| `weak` \| `fair` \| `strong` \| `very_strong`	Strength rating based on entropy
`crack_time_offline_fast_seconds`	number	Estimated seconds to crack at 10¹⁰ guesses/sec (fast offline attack)

Privacy

The password is transmitted over HTTPS and is not stored or logged.

API Reference

Endpoint

POST https://api.lightningapi.tools/password-entropy

Required headers

Authorization: Bearer <apiKey>
Content-Type: application/json

Example request

{
  "password": "horse.correct-battery$taple"
}

Example response

{
  "length": 26,
  "charset_size": 94,
  "charset": {
    "lowercase": true,
    "uppercase": false,
    "digits": false,
    "symbols": true
  },
  "entropy_bits": 170.3,
  "strength": "very_strong",
  "crack_time_offline_fast_seconds": 1e+60
}