Solidity Function Selector Calculator — Free & Private

A free edge API by formatho.com, privacy-first developer tools.

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Free, no signup, runs entirely in your browser — your data never leaves your device.

🔓 Free🔒 Zero tracking🚫 No data collection⚡ Edge-fast

Usage

curl "https://function-selector-formatho.filesformatho.workers.dev/api?sig=transfer(address,uint256)"
# → { "selector": "a9059cbb", "selector_0x": "0xa9059cbb", "keccak256": "a9059cbb…", ... }

curl "https://function-selector-formatho.filesformatho.workers.dev/api?sig=transfer(address,uint256)%0Aapprove(address,uint256)"   # bulk: newline-separated

The selector is the first 4 bytes of keccak256 of the canonical signature; the full 32-byte hash is the event topic0. GET or POST JSON — {"sig": "…"} or {"sigs": ["…"]}, up to 50 signatures per request. Pass signatures without spaces, exactly as Solidity canonicalizes them.

Full parameter reference: /api endpoint.

Privacy-first: signatures are hashed in-memory at the edge and never logged or stored.

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Compute selectors entirely client-side: Function Selector Calculator on formatho.com.

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