# event_signature_json

Returns EVM topic0 for an event described by JSON ABI; use it to filter or validate non-anonymous logs.

Canonical HTML: <https://determica.com/docs/functions/event_signature_json>

- Kind: scalar function
- Category: [Contracts and ABI](/docs/category/contracts-and-abi.md)
- Tags: ABI

Returns EVM topic0 for an event described by JSON ABI; use it to filter or validate non-anonymous logs.

## Overload 1: event_signature_json(JSON)

```sql
event_signature_json(JSON)
```

Builds the canonical event signature from JSON ABI inputs before hashing with Keccak-256.

- Kind: scalar
- Execution context: Offline
- Behavior: Canonical Json Event Signature
- Execution modes: Offline
- Input shape: Scalar Arguments
- Planning contract: Runtime
- Cardinality: One Per Input
- Determinism: Deterministic
- Return shape: Scalar
- Schema stability: Fixed
- Stability: Stable
- Side effects: None documented

### Inputs

- `abi` (JSON; required; positional) — A single event ABI object with name and inputs. Indexed flags do not change the topic0 signature hash.

### Returns

Event topic0

Keccak-256 of the canonical event signature as BYTES32.

- `signature` (BYTES32)

Event topic0. Keccak-256 of the canonical event signature as BYTES32.

### Examples

_Local SQL · Local_

```sql
-- topic0 of the ERC-20 Transfer event from its JSON ABI entry
SELECT event_signature_json(json('{
    "type": "event",
    "name": "Transfer",
    "inputs": [
        {"indexed": true, "name": "from", "type": "address"},
        {"indexed": true, "name": "to", "type": "address"},
        {"indexed": false, "name": "value", "type": "uint256"}
    ]
}')) AS topic0;
-- ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef
```

## Guidance

### Selector, topic0, calldata, and return data

Use event_signature or event_signature_json to build topic0 before filtering logs or validating decoded events. The JSON helper derives canonical input types and ignores names and indexed modifiers.

- Anonymous logs omit topic0 even though this helper can still compute the event signature hash.
- Indexed flags affect where values appear in log topics, but not the event signature hash.
- The Transfer example is the USDC log at Ethereum block 20,000,000, transaction 0x5cbf...3dde, log index 97; its topics and data are reconstructed offline.
- Use function_selector for the first four bytes of calldata.
- Use error_selector for the first four bytes of custom error revert data.
- Use event_decode_json when you already have topics and data to decode.

```sql
SELECT event_signature('Transfer(address,address,uint256)') AS topic0;
```

## Related functions

- [get_logs](/docs/functions/get_logs.md) — Usually Before
- [event_decode](/docs/functions/event_decode.md) — Usually Before
- [event_decode_json](/docs/functions/event_decode_json.md) — Usually Before
- [parse_abi_event](/docs/functions/parse_abi_event.md) — See Also