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Reading an address

7 min read

Addresses starting with 1, 3, bc1q or bc1p encode different script types and eras. All are checked with a built-in checksum before use.

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Answer every question correctly (100%) to complete this lesson.

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Four common prefixes exist on Bitcoin mainnet. Addresses starting with '1' are P2PKH (pay to public key hash), the original 2009 format. Addresses starting with '3' are P2SH (pay to script hash), introduced in 2012, historically used for multisig and later for wrapped segwit. Addresses starting with 'bc1q' are native SegWit (P2WPKH/P2WSH, 2017), using the bech32 encoding. Addresses starting with 'bc1p' are Taproot (P2TR, 2021), using the newer bech32m encoding.

Every format includes a built-in checksum: a short piece of data mathematically derived from the rest of the address. Wallets recompute it before sending, so a mistyped or corrupted address is rejected rather than silently sending funds to a wrong destination, this protects against typos, not against sending to the wrong-but-valid address.

Bech32 and bech32m addresses use only lowercase letters and digits, deliberately excluding visually confusing characters like '1', 'b', 'i', 'o'. Newer formats generally produce smaller transactions and lower fees, which is why wallets increasingly default to bc1q or bc1p addresses.

Testnet, a separate network used for development and testing with worthless coins, uses its own prefixes (commonly starting with 'm', 'n', '2' or 'tb1'), which are never valid on the real network. Sending mainnet coins to a testnet-looking address, or vice versa, will typically be rejected by a correctly built wallet, but the format itself is the visual clue to check.

Explain more simply

Bitcoin addresses look like random text, but the first characters actually tell you what type of address it is and roughly how old that format is.

You never need to type an address by hand, copy-paste or scan a QR code, and the wallet checks it automatically for typos before sending.

Real-world analogy

Address prefixes are like postcode formats from different eras of the postal system: all still deliver mail, but the newer ones were designed to be harder to misread and cheaper to sort.

Key facts

  • Prefixes 1, 3, bc1q and bc1p mark P2PKH, P2SH, native SegWit and Taproot addresses respectively.
  • Every address format has a built-in checksum that catches typos before broadcast.
  • Testnet addresses use distinct prefixes and are never valid on mainnet.

Common misconception

“An address starting with '1' is old and less secure than a newer 'bc1' address.”

The cryptography behind spending is equally secure across formats. What differs is transaction efficiency (fees) and error-detection quality, not the security of the underlying keys.[4]

Go deeper

P2PKH and P2SH addresses use Base58Check encoding with a 4-byte checksum from a double SHA-256 hash. Bech32 (BIP-173) and bech32m (BIP-350) instead use a different error-correcting code that can detect many more error patterns and also enables reliable QR/voice transcription.

Because address type reveals the script template but not the exact spending policy, two P2SH addresses can hide entirely different scripts, one might be a 2-of-3 multisig, another an old wrapped-segwit single key. The address alone never proves what conditions guard the funds.

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.What does an address prefix like 'bc1p' indicate?

    What does an address prefix like 'bc1p' indicate?

  2. 2.What does an address checksum protect against?

    What does an address checksum protect against?

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Extra exam questions

Every question here counts towards your accuracy, XP and rank. No guessing: every answer is explained.

16 questions

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.A Bitcoin address starting with '1' is which type?

    A Bitcoin address starting with '1' is which type?

  2. 2.An address starting with '3' typically represents which script type?

    An address starting with '3' typically represents which script type?

  3. 3.Native SegWit P2WPKH addresses on mainnet start with which prefix?

    Native SegWit P2WPKH addresses on mainnet start with which prefix?

  4. 4.Taproot addresses on mainnet start with which prefix?

    Taproot addresses on mainnet start with which prefix?

  5. 5.What encoding scheme do bech32 and bech32m addresses use instead of Base58Check?

    What encoding scheme do bech32 and bech32m addresses use instead of Base58Check?

  6. 6.Why do legacy Base58Check addresses exclude characters like 0, O, I, and l?

    Why do legacy Base58Check addresses exclude characters like 0, O, I, and l?

  7. 7.What is the main purpose of a checksum embedded in a Bitcoin address?

    What is the main purpose of a checksum embedded in a Bitcoin address?

  8. 8.If you change a single character in a valid Bitcoin address, what usually happens?

    If you change a single character in a valid Bitcoin address, what usually happens?

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Sources