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+---
+description: Custom Errors for ENSIP-10 
+contributors:
+  - raffy.eth
+ensip:
+  created: '2025-03-01'
+  status: draft
+---
+
+# ENSIP-X: Custom Errors for ENSIP-10
+
+## Abstract
+
+This standard establishes [custom errors](https://docs.soliditylang.org/en/latest/contracts.html#custom-errors) for [ENSIP-10](./10.md) `resolve()` to improve the resolution experience and disambiguate the following situations:
+
+* the [resolver profile](https://github.com/ensdomains/ens-contracts/tree/staging/contracts/resolvers/profiles) (eg. `contenthash()`) is not supported
+* the name (eg. `nick.eth`) does not exist
+* all other resolution errors
+
+## Motivation
+
+ENS and the broader Ethereum ecosystem are becoming increasingly multichain.  [ERC-3668](https://eips.ethereum.org/EIPS/eip-3668) enables offchain access and ENSIP-10 allows a complete namespace to be bridged from another chain.
+
+Currently, it is difficult to programmatically disambiguate between resolution responses that have different end-user consequences.  Clients are forced to interpret `null` and resolution reverts as *this record does not exist*.  There is no reliable technique to check if a name exists.
+
+## Specification
+
+An ENSIP-10 enabled contract SHOULD utilize the following errors:
+
+### UnsupportedResolverProfile
+
+```solidity
+/// @param selector Function selector of the resolver profile that cannot be answered.
+error UnsupportedResolverProfile(bytes4 selector);
+```
+
+Selector: [`0x7b1c461b`](https://adraffy.github.io/keccak.js/test/demo.html#algo=evm&s=UnsupportedResolverProfile%28bytes4%29&escape=1&encoding=utf8)
+
+This error should be raised when the selector of supplied `calldata` corresponds to an unsupported resolver profile.
+
+### UnreachableName
+
+```solidity
+/// @param name DNS-encoded ENS name that does not exist.
+error UnreachableName(bytes name);
+```
+
+Selector: [`0x5fe9a5df`](https://adraffy.github.io/keccak.js/test/demo.html#algo=evm&s=UnreachableName%28bytes%29&escape=1&encoding=utf8)
+
+This error should be raised when the supplied `name` does not exist, which could happen for a variety of reasons:
+
+* incorrectly encoded
+* cannot be parsed — eg. `zzz.3c.reverse` where `zzz` is expected to be 40 hexadecimal characters.
+* does not exist — eg. `__dne.base.eth` where `__dne` is not a registered [Basename](https://www.base.org/names).
+
+When existence is unknown, a `null` response is preferable to a false-positive revert.
+
+When this error is raised, all responses for `name` are effectively `null`.
+
+### Revert Priority
+
+ENSIP-10 [states](./10.md#specification) *"the function MUST either return valid return data for that function, or revert if it is not supported."*  When both errors apply, `UnsupportedResolverProfile` MUST be raised before `UnreachableName`.
+
+## Rationale
+
+The proposed implementation makes it possible to check for extended resolver profile support, similar to [ERC-165](https://eips.ethereum.org/EIPS/eip-165).
+
+When queried with a supported resolver profile, the existence of a name can be determined by the presence of `UnreachableName`.
+
+Clients can utilize this information to improve the resolution experience.  All other errors likely correspond to unexpected resolution failures.
+
+## Backwards Compatibility
+
+This proposal does not alter the resolution process, it only supplies additional error information when a name cannot be resolved.
+
+* Resolvers that return `null` when queried with an unsupported resolver profile should be redeployed.
+* Resolvers that follow this specification but raise a different error do not require redeployment.
+
+## Security Considerations
+
+None.
+
+## Copyright
+
+<!-- Just leave this how it is -->
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).