Keywords

The complete reference guide to all Clarity keywords.

The Nakamoto hard fork will introduce a few new Clarity keywords. It's important to note that even with the new block production mechanism, the block-height keyword behavior will not change. It will simply correspond to the current tenure height. This means any Clarity contracts using this keyword will be backwards compatible after the Nakamoto Upgrade.

block-height

Introduced in: Clarity 1

output: uint

description:

Returns the current block height of the Stacks blockchain in Clarity 1 and 2. Upon activation of epoch 3.0, block-height will return the same value as tenure-height. In Clarity 3, block-height is removed and has been replaced with stacks-block-height.

example:

(> block-height u1000) ;; returns true if the current block-height has passed 1000 blocks.

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burn-block-height

There is a bug in Clarity 3 when burn-block-height is used within an at-block expression. Normally, keywords executed within an at-block expression will return the data for that specified block. This bug causes burn-block-height always to return the burn block at the current chain tip, even within an at-block expression. This behavior affects any Clarity 3 contracts and will be fixed in a future hard fork.

Introduced in: Clarity 1

output: uint

description:

Returns the current block height of the underlying burn blockchain as a uint

example:

(> burn-block-height 1000) ;; returns true if the current height of the underlying burn blockchain has passed 1000 blocks.

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chain-id

Introduced in: Clarity 2

output: uint

description:

Returns the 32-bit chain ID of the blockchain running this transaction

example:

(print chain-id) ;; Will print 'u1' if the code is running on mainnet, and 'u2147483648' on testnet, and other values on different chains.

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contract-caller

Introduced in: Clarity 1

output: principal

description:

Returns the caller of the current contract context. If this contract is the first one called by a signed transaction, the caller will be equal to the signing principal. If contract-call? was used to invoke a function from a new contract, contract-caller changes to the calling contract's principal. If as-contract is used to change the tx-sender context, contract-caller also changes to the same contract principal.

example:

(print contract-caller) ;; Will print out a Stacks address of the transaction sender

Use caution when leveraging all contract calls, particularly tx-sender and contract-caller as based on the design, you can unintentionally introduce attack surface area. Read more.

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current-contract

Introduced in: Clarity 4

output: principal

description: Returns the principal of the current contract.

example:

(stx-transfer? u1000000 tx-sender current-contract)

---

false

Introduced in: Clarity 1

output: bool

description:

Boolean false constant.

example:

(and true false) ;; Evaluates to false
(or false true)  ;; Evaluates to true

---

is-in-mainnet

Introduced in: Clarity 2

output: bool

description:

Returns a boolean indicating whether or not the code is running on the mainnet

example:

(print is-in-mainnet) ;; Will print 'true' if the code is running on the mainnet

---

is-in-regtest

Introduced in: Clarity 1

output: bool

description:

Returns whether or not the code is running in a regression test

example:

(print is-in-regtest) ;; Will print 'true' if the code is running in a regression test

---

none

Introduced in: Clarity 1

output: (optional ?)

description:

Represents the none option indicating no value for a given optional (analogous to a null value).

example:

(define-public (only-if-positive (a int))
  (if (> a 0)
      (some a)
      none))
(only-if-positive 4) ;; Returns (some 4)
(only-if-positive (- 3)) ;; Returns none

(print stx-liquid-supply) ;; Will print out the total number of liqui

---

stacks-block-height

Introduced in: Clarity 3

output: uint

description:

Returns the current Stacks block height.

example:

(print stacks-block-height) ;; Will print out the current Stacks block height

---

stacks-block-time

Introduced in: Clarity 4

output: uint

description: Returns the timestamp of the current block in seconds since the Unix epoch

This same timestamp can also be retrieved for previous blocks using (get-stacks-block-info? time height), which exists since Clarity 3, but cannot be used for the current block.

Note that stacks-block-time will properly account for the context of an at-block expression. If the at-block sets the context to a block that is from before Clarity 4 has activated, attempting to use stacks-block-time in that context will result in a runtime error.

(if (> stacks-block-time 1755820800)
  (print "after 2025-07-22")
  (print "before 2025-07-22"))

---

stx-liquid-supply

Introduced in: Clarity 1

output: uint

description:

Returns the total number of micro-STX (uSTX) that are liquid in the system as of this block.

example:

(print stx-liquid-supply) ;; Will print out the total number of liquid uSTX

---

tenure-height

Introduced in: Clarity 3

output: uint

description:

Returns the number of tenures that have passed. When the Nakamoto block-processing starts, this will be equal to the chain length.

example:

(print tenure-height) ;; Will print out the current tenure height

---

true

Introduced in: Clarity 1

output: bool

description:

Boolean true constant.

example:

(and true false) ;; Evaluates to false
(or false true)  ;; Evaluates to true

---

tx-sender

Introduced in: Clarity 1

output: principal

description:

Returns the original sender of the current transaction, or if as-contract was called to modify the sending context, it returns that contract principal.

example:

(print tx-sender) ;; Will print out a Stacks address of the transaction sender

Use caution when leveraging all contract calls, particularly tx-sender and contract-caller as based on the design, you can unintentionally introduce attack surface area. Read more.

---

tx-sponsor?

Introduced in: Clarity 2

output: optional principal

description:

Returns the sponsor of the current transaction if there is a sponsor, otherwise returns None.

example:

(print tx-sponsor?) ;; Will print out an optional value containing the Stacks address of the transaction sponsor