Bitcoin Address Formats

Bitcoin addresses have evolved through four major formats. Agents must recognize and handle all types to interact with the full Bitcoin ecosystem.

Address Types at a Glance

Type	Prefix	Length	Encoding	Introduced
P2PKH (Legacy)	1	25-34 chars	Base58Check	2009
P2SH (Script)	3	34 chars	Base58Check	2012 (BIP-16)
P2WPKH (SegWit v0)	bc1q	42 chars	Bech32	2017 (BIP-141)
P2TR (Taproot)	bc1p	62 chars	Bech32m	2021 (BIP-341)

P2PKH (Pay-to-Public-Key-Hash)

Prefix: 1 (mainnet), m or n (testnet)

The original Bitcoin address format. Pays to the hash of a public key.

Example: 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa
         ↑
         Always starts with 1

Structure

Version (1 byte) + RIPEMD160(SHA256(pubkey)) (20 bytes) + Checksum (4 bytes)

Agent Notes

• Highest transaction fees (largest witness data)
• Still widely used, must support for compatibility
• Satoshi’s genesis block address uses this format

P2SH (Pay-to-Script-Hash)

Prefix: 3 (mainnet), 2 (testnet)

Pays to the hash of a script. Enables multisig and wrapped SegWit.

Example: 3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy
         ↑
         Always starts with 3

Use Cases

• Multisig wallets: 2-of-3, 3-of-5 signing schemes
• Wrapped SegWit (P2SH-P2WPKH): SegWit compatibility for old wallets
• Complex scripts: Time-locked contracts, hash locks

Agent Notes

• When you see 3..., it could be multisig OR wrapped SegWit
• Cannot determine spending conditions from address alone
• Medium fees (between P2PKH and native SegWit)

P2WPKH (Native SegWit v0)

Prefix: bc1q (mainnet), tb1q (testnet)

Native Segregated Witness address. Recommended for most use cases.

Example: bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq
         ↑↑↑↑
         bc1q prefix (q = version 0)

Benefits

• Lower fees: ~30-40% cheaper than P2PKH
• Error detection: Bech32 encoding catches typos
• Malleability fix: Transaction IDs cannot be modified

Bech32 Encoding

• Uses 32-character alphabet: qpzry9x8gf2tvdw0s3jn54khce6mua7l
• Case insensitive (but lowercase preferred)
• Includes error-correcting checksum

Agent Notes

• Recommended for receiving payments
• Supported by all modern wallets (2024+)
• Parse with Bech32 library, not Base58

P2TR (Taproot)

Prefix: bc1p (mainnet), tb1p (testnet)

Taproot address (SegWit v1). Most advanced format with privacy and smart contract benefits.

Example: bc1p5d7rjq7g6rdk2yhzks9smlaqtedr4dekq08ge8ztwac72sfr9rusxg3297
         ↑↑↑↑
         bc1p prefix (p = version 1)

Benefits

• Privacy: Single-sig and multi-sig look identical on-chain
• Efficiency: Complex scripts revealed only when needed
• Schnorr signatures: Aggregatable, smaller, faster

Bech32m Encoding

• Modified Bech32 for SegWit v1+
• Different checksum constant than Bech32
• Use BIP-350 compliant libraries

Agent Notes

• Best for privacy-sensitive operations
• Supports advanced scripting (Tapscript)
• Requires newer wallet software

Address Validation

Regex Patterns

// Mainnet address patterns
const patterns = {
  p2pkh: /^1[a-km-zA-HJ-NP-Z1-9]{25,34}$/,
  p2sh: /^3[a-km-zA-HJ-NP-Z1-9]{33}$/,
  p2wpkh: /^bc1q[a-z0-9]{38,39}$/,
  p2tr: /^bc1p[a-z0-9]{58}$/
};

// Testnet patterns
const testnetPatterns = {
  p2pkh: /^[mn][a-km-zA-HJ-NP-Z1-9]{25,34}$/,
  p2sh: /^2[a-km-zA-HJ-NP-Z1-9]{33}$/,
  p2wpkh: /^tb1q[a-z0-9]{38,39}$/,
  p2tr: /^tb1p[a-z0-9]{58}$/
};

Validation Steps

1. Check prefix to determine type
2. Validate length for expected range
3. Verify checksum (Base58Check or Bech32/m)
4. Decode to extract pubkey hash or script hash

# Python example using bitcoinlib
from bitcoin import decode_address

def validate_address(address):
    try:
        result = decode_address(address)
        return {
            "valid": True,
            "type": result.type,
            "network": result.network
        }
    except:
        return {"valid": False}

API Response Handling

When querying blockchain APIs, addresses may be returned in different formats:

// mempool.space UTXO response
{
  "txid": "abc123...",
  "vout": 0,
  "value": 100000,
  "address": "bc1q..."  // May be any format
}

Agent Strategy

1. Store addresses in their original format
2. Validate format before using
3. Use SegWit (bc1q) when generating new addresses
4. Accept all formats when receiving payments

Fee Comparison

Transaction size by address type (single input, two outputs):

Type	Virtual Bytes	Fee at 10 sat/vB
P2PKH	~226 vB	2,260 sats
P2SH-P2WPKH	~167 vB	1,670 sats
P2WPKH	~141 vB	1,410 sats
P2TR	~111 vB	1,110 sats

Recommendation: Use P2TR or P2WPKH for optimal fees.

Network Prefixes Summary

Network	P2PKH	P2SH	Bech32 HRP
Mainnet	1	3	bc
Testnet	m/n	2	tb
Signet	m/n	2	tb
Regtest	m/n	2	bcrt

---

Machine-Readable Summary

{
  "topic": "bitcoin-address-formats",
  "address_types": [
    {"type": "p2pkh", "prefix": "1", "encoding": "base58check"},
    {"type": "p2sh", "prefix": "3", "encoding": "base58check"},
    {"type": "p2wpkh", "prefix": "bc1q", "encoding": "bech32"},
    {"type": "p2tr", "prefix": "bc1p", "encoding": "bech32m"}
  ],
  "recommendation": "p2wpkh",
  "validation_libraries": ["bitcoinjs-lib", "python-bitcoinlib", "rust-bitcoin"]
}