Aborting Execution

A transaction can either succeed or fail. Successful execution applies all the changes made to objects and on-chain data, and the transaction is committed to the blockchain. Alternatively, if a transaction aborts, the changes are not applied. The abort keyword is used to abort a transaction and revert the changes made so far.

It is important to note that there is no catch mechanism in Move. If a transaction aborts, the changes made so far are reverted, and the transaction is considered failed.


The abort keyword is used to abort the execution of a transaction. It is used in combination with an abort code, which will be returned to the caller of the transaction. The abort code is an integer of type u64.

let user_has_access = true;

// abort with a predefined constant if `user_has_access` is false
if (!user_has_access) {
    abort 0

// there's an alternative syntax using parenthesis`
if (user_has_access) {

The code above will, of course, abort with abort code 1.


The assert! macro is a built-in macro that can be used to assert a condition. If the condition is false, the transaction will abort with the given abort code. The assert! macro is a convenient way to abort a transaction if a condition is not met. The macro shortens the code otherwise written with an if expression + abort. The code argument is required and has to be a u64 value.

// aborts if `user_has_access` is `false` with abort code 0
assert!(user_has_access, 0);

// expands into:
if (!user_has_access) {
    abort 0

Error constants

To make error codes more descriptive, it is a good practice to define error constants. Error constants are defined as const declarations and are usually prefixed with E followed by a camel case name. Error constants are no different from other constants and don't have special handling, however, they are used to increase the readability of the code and make it easier to understand the abort scenarios.

/// Error code for when the user has no access.
const ENoAccess: u64 = 0;
/// Trying to access a field that does not exist.
const ENoField: u64 = 1;

/// Updates a record.
public fun update_record(/* ... , */ user_has_access: bool, field_exists: bool) {
    // asserts are way more readable now
    assert!(user_has_access, ENoAccess);
    assert!(field_exists, ENoField);

    /* ... */

Further reading