OP Codes

The instruction set for Bitcoin. Bitcoin Script uses a stack-based programming language with various opcodes (operation codes) that perform different functions. This document provides a complete reference of Bitcoin OP codes with explanations and code examples. Try these opcodes in Stack Lab.

OP Code Categories

Category	Description	Examples
Stack Operations	Manipulate the stack	OP_DUP, OP_DROP, OP_SWAP
Arithmetic	Mathematical operations	OP_ADD, OP_SUB
Cryptographic	Hash functions and signatures	OP_SHA256, OP_CHECKSIG
Comparison	Test conditions	OP_EQUAL, OP_LESSTHAN
Control Flow	Conditional execution	OP_IF, OP_ELSE
Time Locks	Transaction timing	OP_CLTV, OP_CSV
Disabled	Removed for security	OP_MUL, OP_CAT

Script Execution Example

Stack Operations

OP Code	Hex	Function
OP_DUP	0x76	Duplicates top stack item
OP_DROP	0x75	Removes top stack item
OP_SWAP	0x7c	Swaps top two items
OP_OVER	0x78	Copies second-to-top to top
OP_ROT	0x7b	Rotates top three items
OP_PICK	0x79	Copies nth item to top
OP_ROLL	0x7a	Moves nth item to top
OP_2DROP	0x6d	Removes top two items
OP_2DUP	0x6e	Duplicates top two items
OP_3DUP	0x6f	Duplicates top three items
OP_NIP	0x77	Removes second-to-top item
OP_TUCK	0x7d	Copies top below second

Examples

OP_DUP:
  Before: [A]
  After:  [A, A]

OP_SWAP:
  Before: [A, B]
  After:  [B, A]

OP_ROT:
  Before: [A, B, C]
  After:  [B, C, A]

Arithmetic Operations

OP Code	Hex	Function	Status
OP_ADD	0x93	a + b	Active
OP_SUB	0x94	a - b	Active
OP_1ADD	0x8b	a + 1	Active
OP_1SUB	0x8c	a - 1	Active
OP_NEGATE	0x8f	-a	Active
OP_ABS	0x90	abs(a)	Active
OP_NOT	0x91	!a (logical)	Active
OP_0NOTEQUAL	0x92	a != 0	Active
OP_MUL	0x95	a * b	Disabled
OP_DIV	0x96	a / b	Disabled
OP_MOD	0x97	a % b	Disabled
OP_LSHIFT	0x98	a << b	Disabled
OP_RSHIFT	0x99	a >> b	Disabled

Note: OP_MUL, OP_DIV, OP_MOD, OP_LSHIFT, and OP_RSHIFT were disabled early in Bitcoin's history to prevent potential denial-of-service attacks through expensive computations.

Comparison Operations

OP Code	Hex	Function
OP_EQUAL	0x87	Returns 1 if equal, else 0
OP_EQUALVERIFY	0x88	OP_EQUAL + OP_VERIFY
OP_LESSTHAN	0x9f	a < b
OP_GREATERTHAN	0xa0	a > b
OP_LESSTHANOREQUAL	0xa1	a <= b
OP_GREATERTHANOREQUAL	0xa2	a >= b
OP_MIN	0xa3	min(a, b)
OP_MAX	0xa4	max(a, b)
OP_WITHIN	0xa5	min <= x < max

Cryptographic Operations

OP Code	Hex	Function
OP_RIPEMD160	0xa6	RIPEMD-160 hash
OP_SHA1	0xa7	SHA-1 hash
OP_SHA256	0xa8	SHA-256 hash
OP_HASH160	0xa9	SHA256 + RIPEMD160
OP_HASH256	0xaa	Double SHA-256
OP_CHECKSIG	0xac	Verify ECDSA signature
OP_CHECKSIGVERIFY	0xad	OP_CHECKSIG + OP_VERIFY
OP_CHECKMULTISIG	0xae	Verify multisig
OP_CHECKMULTISIGVERIFY	0xaf	OP_CHECKMULTISIG + OP_VERIFY

Bitwise Operations (Disabled)

OP Code	Hex	Function	Status
OP_AND	0x84	Bitwise AND	Disabled
OP_OR	0x85	Bitwise OR	Disabled
OP_XOR	0x86	Bitwise XOR	Disabled
OP_INVERT	0x83	Bitwise NOT	Disabled

These were disabled to prevent potential vulnerabilities in early Bitcoin.

Control Flow

OP Code	Hex	Function
OP_IF	0x63	Execute if top is non-zero
OP_NOTIF	0x64	Execute if top is zero
OP_ELSE	0x67	Else branch
OP_ENDIF	0x68	End conditional
OP_VERIFY	0x69	Fail if top is false
OP_RETURN	0x6a	Mark output unspendable

Conditional Example

<condition>
OP_IF
    <execute if true>
OP_ELSE
    <execute if false>
OP_ENDIF

Time Lock Operations

OP_CHECKLOCKTIMEVERIFY (CLTV)

Code: 0xb1

Verifies the transaction's nLockTime is at least the specified value (absolute time lock).

<locktime> OP_CHECKLOCKTIMEVERIFY OP_DROP <pubkey> OP_CHECKSIG

Use cases:

Payment channels
Time-locked savings
Inheritance planning

OP_CHECKSEQUENCEVERIFY (CSV)

Code: 0xb2

Verifies the input's sequence number enforces a relative time lock.

<relative_locktime> OP_CHECKSEQUENCEVERIFY OP_DROP <pubkey> OP_CHECKSIG

Use cases:

Lightning Network HTLCs
Escrow with timeout
Revocable transactions

Push Operations

OP Code	Hex	Function
OP_0 / OP_FALSE	0x00	Push empty array (false)
OP_1NEGATE	0x4f	Push -1
OP_1 / OP_TRUE	0x51	Push 1
OP_2 - OP_16	0x52-0x60	Push 2-16
OP_PUSHDATA1	0x4c	Next byte is length
OP_PUSHDATA2	0x4d	Next 2 bytes are length
OP_PUSHDATA4	0x4e	Next 4 bytes are length

Tapscript Opcodes (BIP 342)

Taproot introduced new opcodes for Tapscript:

OP_CHECKSIGADD

Code: 0xba

Enables efficient Schnorr signature aggregation for multisig.

<pubkey1> OP_CHECKSIG
<pubkey2> OP_CHECKSIGADD
<pubkey3> OP_CHECKSIGADD
<threshold> OP_NUMEQUAL

Benefits over OP_CHECKMULTISIG:

No dummy element needed
More efficient batch validation
Works with Schnorr signatures

OP_SUCCESS Opcodes

Codes 0x50, 0x62, 0x89-0x8a, 0x8d-0x8e, 0x95-0x99, 0xbb-0xfe

Reserved for future upgrades. Any script containing these immediately succeeds, allowing soft fork upgrades.

Disabled Opcodes

These opcodes were disabled for security reasons:

OP Code	Hex	Reason
OP_CAT	0x7e	Could create oversized scripts
OP_SUBSTR	0x7f	Security concerns
OP_LEFT	0x80	Security concerns
OP_RIGHT	0x81	Security concerns
OP_INVERT	0x83	Security concerns
OP_AND	0x84	Security concerns
OP_OR	0x85	Security concerns
OP_XOR	0x86	Security concerns
OP_2MUL	0x8d	Can be done with OP_ADD
OP_2DIV	0x8e	Security concerns
OP_MUL	0x95	Expensive computation
OP_DIV	0x96	Division by zero issues
OP_MOD	0x97	Division by zero issues
OP_LSHIFT	0x98	Could create large numbers
OP_RSHIFT	0x99	Security concerns

OP_CAT Revival: There is ongoing discussion about re-enabling OP_CAT with proper limits, as it would enable new use cases like covenants.

Common Script Patterns

P2PKH (Pay-to-Pubkey-Hash)

Locking Script (scriptPubKey):
OP_DUP OP_HASH160 <pubkeyhash> OP_EQUALVERIFY OP_CHECKSIG

Unlocking Script (scriptSig):
<signature> <publickey>

P2SH (Pay-to-Script-Hash)

Locking Script:
OP_HASH160 <scripthash> OP_EQUAL

Unlocking Script:
<data> ... <redeemscript>

Multisig (2-of-3)

Locking Script:
OP_2 <pubkey1> <pubkey2> <pubkey3> OP_3 OP_CHECKMULTISIG

Unlocking Script:
OP_0 <sig1> <sig2>

Note: OP_0 is required due to a bug in OP_CHECKMULTISIG that pops one extra item.

HTLC (Hash Time-Locked Contract)

OP_IF
    OP_SHA256 <hash> OP_EQUALVERIFY
    <receiver_pubkey> OP_CHECKSIG
OP_ELSE
    <timeout> OP_CHECKLOCKTIMEVERIFY OP_DROP
    <sender_pubkey> OP_CHECKSIG
OP_ENDIF

Script Limits

Limit	Value	Purpose
Max script size	10,000 bytes	Prevent oversized scripts
Max stack size	1,000 items	Prevent stack overflow
Max item size	520 bytes	Prevent oversized items
Max ops per script	201	Prevent expensive scripts
Max multisig keys	20	Limit signature checks
Max Tapscript size	No limit*	Weight-based limits apply

*Tapscript has no explicit size limit but is constrained by block weight.

OP Code Quick Reference

Hex	Name	Description	Status
0x00	OP_0	Push empty array	Active
0x4f	OP_1NEGATE	Push -1	Active
0x51-0x60	OP_1-OP_16	Push 1-16	Active
0x63	OP_IF	Conditional	Active
0x64	OP_NOTIF	Conditional	Active
0x67	OP_ELSE	Conditional	Active
0x68	OP_ENDIF	Conditional	Active
0x69	OP_VERIFY	Verify	Active
0x6a	OP_RETURN	Data carrier	Active
0x75	OP_DROP	Remove top	Active
0x76	OP_DUP	Duplicate top	Active
0x77	OP_NIP	Remove second	Active
0x78	OP_OVER	Copy second	Active
0x79	OP_PICK	Copy nth	Active
0x7a	OP_ROLL	Move nth	Active
0x7b	OP_ROT	Rotate 3	Active
0x7c	OP_SWAP	Swap 2	Active
0x7d	OP_TUCK	Tuck top	Active
0x7e	OP_CAT	Concatenate	Disabled
0x84	OP_AND	Bitwise AND	Disabled
0x85	OP_OR	Bitwise OR	Disabled
0x86	OP_XOR	Bitwise XOR	Disabled
0x87	OP_EQUAL	Equality	Active
0x88	OP_EQUALVERIFY	Equal + verify	Active
0x93	OP_ADD	Addition	Active
0x94	OP_SUB	Subtraction	Active
0x95	OP_MUL	Multiplication	Disabled
0x96	OP_DIV	Division	Disabled
0x97	OP_MOD	Modulo	Disabled
0xa6	OP_RIPEMD160	RIPEMD160	Active
0xa7	OP_SHA1	SHA1	Active
0xa8	OP_SHA256	SHA256	Active
0xa9	OP_HASH160	SHA256+RIPEMD160	Active
0xaa	OP_HASH256	Double SHA256	Active
0xac	OP_CHECKSIG	Check signature	Active
0xae	OP_CHECKMULTISIG	Check multisig	Active
0xb1	OP_CLTV	Absolute timelock	Active
0xb2	OP_CSV	Relative timelock	Active
0xba	OP_CHECKSIGADD	Tapscript multisig	Active

Script System: How Bitcoin Script works
OP_RETURN Debate: Controversy about data storage
Taproot - Schnorr signatures and Tapscript

Resources

Bitcoin Wiki: Script: Complete script reference
BIP 342: Tapscript: Tapscript specification
Learn Me a Bitcoin: Script: Visual script explanations