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Security patterns · medium

25. Custom error messages and revert reasons

Writing informative, gas-conscious revert strings.

1 min read3 questionsup to 50 XPtopic 25/50

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Vyper doesn't support Solidity's typed custom errors; string messages attached to `assert`/`raise` are the whole mechanism. Keep them short — every character is calldata/bytecode you pay for — but specific enough to debug quickly.

@external
def transfer(to: address, amount: uint256):
    assert to != empty(address), "zero address"
    assert self.balances[msg.sender] >= amount, "insufficient balance"
    self.balances[msg.sender] -= amount
    self.balances[to] += amount

`empty(address)` produces the zero address in a readable way, and is the idiomatic Vyper equivalent of Solidity's `address(0)`.

How to study this topic

  1. 1. Read the explanation once end to end, skipping the code.
  2. 2. Re-read the code snippets and say out loud what each line does.
  3. 3. Answer the quiz without scrolling back — that is the real check.
  4. 4. Read every explanation, even for the answers you got right.

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Check your understanding

  1. 1. Does Vyper support Solidity-style custom error types (error Foo())?

  2. 2. What produces the zero address in Vyper?

  3. 3. Why keep revert strings short?

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