What Is a Seed Phrase?

A seed phrase, also called a recovery phrase or mnemonic, is a list of usually 12 or 24 words that acts as the master backup for a crypto wallet: from it, a wallet can regenerate all of your private keys and addresses on any compatible device. Whoever knows the seed phrase controls the funds, which is why it must be kept offline and never shared.

When you create a self-custody wallet, the app or device shows you these words once and asks you to write them down. Many beginners treat this as a formality. It is actually the most important moment in owning crypto yourself, because there is no password reset, no support line and no bank that can restore your access if the words are lost or stolen.

How a Seed Phrase Works

Behind the scenes, a wallet starts by generating a large random number. That randomness is turned into words so humans can write it down accurately:

1. 1The wallet generates random data, typically 128 bits for a 12-word phrase or 256 bits for 24 words.
2. 2A short checksum is added so wallets can detect most typos.
3. 3The result is split into chunks, and each chunk maps to a word from a standard list of 2,048 words.
4. 4The words are converted into a seed, from which the wallet derives a tree of private keys, one for each address.

This system of deriving many keys from one seed is called a hierarchical deterministic (HD) wallet. It is why one phrase can restore addresses for Bitcoin, Ethereum and other networks in a multi-chain wallet. The exact addresses depend on settings called derivation paths, which is why restoring in a different wallet app occasionally shows different addresses at first.

Why the word list matters

The BIP-39 list is designed so that the first four letters of each word are unique. That is why many metal backups store only four letters per word. It also means a word that is not on the list is a sign of a typo.

Seed Phrase vs Private Key vs Password

Our explainer on public keys vs private keys covers the cryptography in more detail.

How to Store a Seed Phrase Safely

Follow these rules from the moment you see the words:

1. 1Write it down by hand, in order, with numbers, on the recovery card or on a metal backup.
2. 2Never store it digitally: no photos, screenshots, cloud notes, email drafts or password managers.
3. 3Check every word for spelling and order before confirming.
4. 4Store it in a secure, private place, separate from your wallet device.
5. 5Consider a second copy in another secure location so one fire or flood cannot destroy both.
6. 6Plan for inheritance so a trusted person could recover the funds if something happened to you.

For durable storage, read our guides to backing up a seed phrase the right way and steel seed phrase backups.

Optional passphrase

Some wallets let you add a passphrase, sometimes called a 25th word. Combined with the seed phrase, it creates an entirely different wallet. It protects you if someone finds your words, but if you forget the passphrase, the funds cannot be recovered.

Seed Phrase Scams to Watch For

Because the seed phrase is the master key, scammers focus on it:

• Fake support agents on social media or chat apps who say they need your phrase to "fix" or "validate" your wallet.
• Phishing websites and pop-ups that imitate a wallet and ask you to "re-sync" by entering your words.
• Fake wallet apps that capture your phrase when you restore.
• Pre-filled recovery cards included with tampered or resold hardware wallets.
• "Airdrop" or "migration" claims requiring you to import your phrase into a new site.

The rule is simple: you only ever type your seed phrase when you yourself choose to restore a wallet on a device or official app you trust. More examples are in our guide to seed phrase scams.

What to Do If Your Seed Phrase Is Exposed

If you think someone has seen your words, act immediately:

1. 1Create a brand-new wallet with a new seed phrase on a trusted device.
2. 2Move all funds from the old wallet to the new one, starting with the most valuable assets.
3. 3Stop using the old wallet entirely.
4. 4Review what else might be compromised, such as your computer or email.

Our checklist on what to do if your wallet is compromised walks through each step.

Bottom line

A seed phrase is the master key to your crypto: a short list of words that can recreate every key in your wallet on any compatible device. Write it down offline, store it securely and separately from your device, never enter it anywhere except a trusted wallet restore, and treat anyone who asks for it as a thief. Getting this one habit right protects you from most self-custody disasters.