Random Password Generator

1. Choose the type. Random characters give the most strength for the length; a passphrase of random words is easier to type on a phone or TV.
2. Set the length and character sets. Length matters most. Turn on the sets the site accepts, and remove look-alike characters if you will read the password aloud or type it by hand.
3. Copy it into your password manager. Press Generate new for another one. The page never stores the password, so save it before you leave.

A random password is a string whose every character (or word) is chosen by a random process, with no pattern a person picked. That makes its strength measurable: it depends only on the length and on how many symbols each position can take.

Human-chosen passwords are different. NIST SP 800-63B notes that people pick predictable passwords, and that composition rules push them to variants such as "Password1!". Attackers try those first, so a password that merely looks complex can fall fast.

A passphrase is a random password made of words. The EFF short wordlist used here has 1,296 words, so each word adds log2(1,296) = 10.34 bits. EFF notes that eight words from this list give about 82 bits.

A random password is not a password manager or a second factor. It solves one problem, guessability; NIST requires services to allow password managers and asks them to permit pasting, which is how a long random password stays usable.

The generator draws each character with the browser's cryptographic random number generator, uses rejection sampling to keep every character equally likely, and computes entropy from the pool size and length.

1. Build the pool from the sets you turned on: 26 lowercase + 26 uppercase + 10 digits + 18 symbols = 80 characters by default.
2. Draw a random number with crypto.getRandomValues, which MDN describes as cryptographically strong and suitable for cryptographic purposes.
3. Reject biased draws. A 32-bit value has 4,294,967,296 outcomes, which is not a multiple of 80. Values at or above the largest multiple of 80 are thrown away and redrawn, so each character has exactly a 1 in 80 chance. Taking the value modulo 80 without this step would favor the first 16 characters slightly.
4. Apply your rules. With "at least one from each set" on, a password missing a set is discarded and regenerated, which keeps all valid passwords equally likely.
5. Compute entropy. 20 x log2(80) = 20 x 6.32 = 126.4 bits. The one-of-each rule removes the passwords that miss a set, about 0.11 bits here, counted exactly by inclusion-exclusion.

Nothing is sent to a server. The random numbers, the password and the entropy all stay on your device, and this page does not store the password.

These figures come from the same formula the tool uses, with the offline attack assumed at 10 billion guesses per second.

Reading the Table

Going from 8 to 16 characters from the same pool does not double the strength; it doubles the bits, from 50.6 to 101.2, which multiplies the guesses by about 1.7 x 10^15 (80 to the 8th power). Length is the lever, which matches the NIST emphasis on length.

The time column is an illustration, not a promise. A slow password hash, such as the "computationally expensive algorithm" NIST prefers, cuts the guess rate by orders of magnitude, while specialized hardware can raise it.

Length, pool size and the rules you add decide the entropy; how the password is stored decides how fast it can be attacked.

Length

Every extra character adds log2(pool) bits: 6.32 bits per character with the 80-character pool. NIST SP 800-63B calls length a primary factor in password strength.

Character Sets

Adding symbols to letters and digits grows the pool from 62 to 80, or 5.95 to 6.32 bits per character. That is less than one extra character is worth, so a longer letters-only password can beat a shorter mixed one.

Removing Look-Alikes

Dropping 0, O, o, 1, l and I shrinks the default pool to 74, costing about 0.11 bits per character. Add a character to make up for it.

One-of-Each and No-Repeat Rules

Both remove some possible passwords, so both lower entropy slightly. The tool counts the loss exactly rather than ignoring it.

Online Versus Offline Attacks

NIST explains that login rate limiting stops fast online guessing, but a stolen list of hashes can be attacked at billions of guesses per second. Offline resistance is what long random passwords buy.

Both are secure when chosen randomly; the choice is about typing and remembering.

Which Should I Choose?

Use random characters for everything your password manager fills in. Use a passphrase for the few secrets you must type or remember, and make it long: EFF recommends six words from its long list for most uses, and notes that eight short-list words give slightly more strength.

Creating or Changing an Account

Generate a new password for every account. CISA advises a different password for each account, at least 16 characters long, so a breach at one site does not unlock others.

After a Breach Notice

NIST says services must force a change when there is evidence a password was compromised. Replace it with a fresh random one, not a small edit of the old one.

Shared or Device Secrets

Wi-Fi keys, router admin passwords and encrypted backups benefit from long random values, since they can often be attacked offline.

Teaching Probability

The entropy formula is a counting problem: 80 choices for each of 20 positions. The combination and permutation calculator shows the same counting rules, and the exponent calculator handles powers like 80^20.

1. Reusing a Password

A strong password used on two sites is only as safe as the weaker site. Generate one per account.

2. Choosing Complexity Over Length

"P@ssw0rd1" looks complex but follows patterns attackers try first. NIST SP 800-63B says services must not impose composition rules, because users respond predictably.

3. Editing a Generated Password by Hand

Swapping characters for a favorite word or date adds a human pattern and does not add real entropy. Generate a longer one instead.

4. Picking Passphrase Words Yourself

Words you choose are far from random. The entropy figure is only true when a random process picks every word.

5. Relying on the Password Alone

Phishing and keyloggers capture any password, long or short. NIST notes these attacks work equally well on lengthy and complex passwords, so turn on multi-factor authentication.

6. Storing It Unsafely

A password in a plain text file or a sticky note undoes the work. Keep it in a reputable password manager.

The entropy shown is exact for how this tool generates passwords: every allowed password is equally likely, so entropy is simply log2 of how many there are.

About the Verdict Bands

The bands are this site's rule of thumb, not a NIST standard: under 40 bits weak, 40 to 59 fair, 60 to 79 strong, 80 or more very strong. NIST SP 800-63B sets password length rules for services rather than entropy targets for users.

The 18 symbols are ! # $ % * + - . / : ; = ? @ ^ _ ~ plus the ampersand. Quote marks, backslash, backtick and space are left out because many forms and command lines mishandle them. To check the large numbers yourself, the logarithm calculator computes log2 of any pool size.

At least 15 characters for a password used on its own, which is the minimum NIST SP 800-63B asks services to require. Longer is better when a password manager fills it in.

Yes. Passwords are made in your browser with crypto.getRandomValues, nothing is sent over the network, and the page does not store them.

Entropy is the number of bits of randomness: log2 of how many passwords the settings could produce. Each extra bit doubles the guesses needed.

This page calls 60 to 79 bits strong and 80 or more very strong. Those bands are a rule of thumb, not a formal standard.

Not for strength. Symbols add less than one extra character does, and NIST says services must not force character mixes. Include them when a site demands them.

Neither is better per bit. A passphrase is easier to type and remember; random characters are shorter for the same strength.

Math.random is not designed for security. crypto.getRandomValues is the browser function built for cryptographically strong random values.

It is the slight unfairness from taking a random number modulo the pool size when the range is not an exact multiple. Rejection sampling removes it.

Not on a schedule. NIST says services must not force periodic changes, but must force a change when there is evidence of compromise.

No. Use a unique password for each account, so one breach cannot unlock the others.

Characters that look alike in many fonts, such as 0 and O or 1, l and I. Removing them helps when you type a password from paper or read it aloud.

From the EFF short wordlist of 1,296 words, published by the Electronic Frontier Foundation under a Creative Commons Attribution license.

• Password length, composition and change rules (Sec. 3.1.1 and Appendix A) (NIST Special Publication 800-63B, 2025).
• Crypto.getRandomValues: cryptographically strong random values (MDN Web Docs).
• Use strong passwords (Cybersecurity and Infrastructure Security Agency; archived page).
• EFF wordlists for random passphrases, 10.3 bits per short-list word (Electronic Frontier Foundation).
• EFF copyright policy, CC BY 4.0 (Electronic Frontier Foundation).