@celo/builder-codes

ERC-8021 builder-code attribution on Celo. One line to tag a transaction; one line to verify it. Wraps ox/erc8021.

Built for, in priority order:

1. MiniPay apps
2. Proof of Ship cohort projects
3. Celo ecosystem projects more broadly

The SDK is Celo-only — examples below all use viem/chains's celo / celoSepolia. Configure your viem clients accordingly.

Install

npm install @celo/builder-codes viem
# or
pnpm add @celo/builder-codes viem
# or
yarn add @celo/builder-codes viem

viem is an optional peer dep, only needed if you call verifyTx.

Local testing without publish: cd sdk && npm pack produces a .tgz you can install with npm install /absolute/path/to/celo-builder-codes-X.Y.Z.tgz (or pnpm add /path/...tgz). The path is absolute and machine-specific, so this is for local-only workflows; for cross-machine sharing, install from npm.

Usage

Tag a transaction

import { toDataSuffix } from "@celo/builder-codes";
import { createWalletClient, http } from "viem";
import { celo } from "viem/chains";

const wallet = createWalletClient({ chain: celo, transport: http() });

await wallet.sendTransaction({
  to: "0x...",
  value: 0n,
  data: toDataSuffix("celo_b7k3p9da"),
});

A note on multi-code: ERC-8021 lets one suffix carry several codes — toDataSuffix(["foo", "bar"]) is supported by the wire format. But each code should only be added by the entity it represents. Your app emits its own code; platform codes like minipay are added by the platform's wallet, not by your app. See BUILDERS.md for the full layering rule.

Verify a transaction

import { verifyTx } from "@celo/builder-codes";
import { createPublicClient, http } from "viem";
import { celo } from "viem/chains";

const client = createPublicClient({ chain: celo, transport: http() });

const result = await verifyTx({ client, hash: "0x..." });
// → { codes: ["celo_b7k3p9da"], schemaId: 0 } or null

Decode a suffix offline

import { fromDataSuffix } from "@celo/builder-codes";

fromDataSuffix("0x63656c6f040080218021802180218021802180218021");
// → { codes: ["celo"], schemaId: 0 }

Wire format

ERC-8021 Schema 0. The suffix layout, reading left-to-right at the end of calldata:

[code:N][length:1][schema:1][marker:16]
                      0x00     0x80218021…×8

Multi-code is encoded as a comma-delimited string in the code field; the SDK splits on decode.

The marker constant is exported as ERC_8021_MARKER.

Validation

toDataSuffix rejects codes that:

• are empty or longer than 32 bytes
• contain anything outside [a-z0-9_] (no uppercase, no spaces, no commas)

This is stricter than ERC-8021 itself but matches the format Celo distributes (celo_xxxxxxxx) and the platform codes used in the Celo ecosystem (minipay, proofofship).

API

toDataSuffix(code: string | readonly string[]): Hex
fromDataSuffix(suffix: Hex): { codes: string[]; schemaId: number } | null
verifyTx({ client, hash }): Promise<{ codes: string[]; schemaId: number } | null>
codeFromHostname(hostname: string): string  // → "celo_xxxxxxxx"

type BuilderCodeSuffix = Hex  // alias for the toDataSuffix return type
ERC_8021_MARKER: "0x80218021802180218021802180218021"

verifyTx never throws — RPC errors return null.

codeFromHostname derives a per-app code from a hostname (used by MiniPay mini apps to self-attribute without a registration step). Algorithm: lowercase → strip leading www. → SHA-256 → first 6 bytes hex (12 chars) → celo_ prefix. Same input → same code, every time. See ../docs/minipay-attribution.md for the design rationale and ../docs/minipay-integration-spec.md for the full MiniPay handover.

Pinned hostname → code vectors

Independently verified against shasum -a 256 and against tests/hostname.test.ts. If a reimplementation doesn't produce these values, the algorithm has drifted.

| Hostname | Code | |---|---| | mondeto.app | celo_b057492a5aa5 | | celo.org | celo_8549372f8229 | | minipay.io | celo_51e519342b9a | | app.mondeto.app | celo_1a8ba29dac7a | | mondeto.vercel.app | celo_04168799c492 |

Subdomains stay distinct by design (so *.vercel.app apps don't all collide into one code). Preview / staging hostnames therefore produce their own codes; aggregate environments at the dashboard layer, not the SDK layer.

License

MIT.