FuelLabs/fuels-ts · error · FuelError

ABI_MAIN_METHOD_MISSING

ABI_MAIN_METHOD_MISSING

Error message

Cannot use ABI without "main" function.

What it means

Thrown by Predicate.processPredicateData when the JSON ABI supplied to a Predicate does not declare a function named 'main'. Fuel predicates must expose a single entrypoint called main that returns a boolean; the SDK uses it to encode configurable constants and to reason about the predicate interface. Without it, the predicate cannot be executed on-chain.

Source

Thrown at packages/account/src/predicate/predicate.ts:215

  /**
   * Processes the predicate data and returns the altered bytecode and interface.
   *
   * @param bytes - The bytes of the predicate.
   * @param jsonAbi - The JSON ABI of the predicate.
   * @param configurableConstants - Optional configurable constants for the predicate.
   * @returns An object containing the new predicate bytes and interface.
   */
  private static processPredicateData(
    bytes: BytesLike,
    jsonAbi: JsonAbi,
    configurableConstants?: { [name: string]: unknown }
  ) {
    let predicateBytes = arrayify(bytes);
    const abiInterface: Interface = new Interface(jsonAbi);

    if (abiInterface.functions.main === undefined) {
      throw new FuelError(
        ErrorCode.ABI_MAIN_METHOD_MISSING,
        'Cannot use ABI without "main" function.'
      );
    }

    if (configurableConstants && Object.keys(configurableConstants).length) {
      predicateBytes = Predicate.setConfigurableConstants(
        predicateBytes,
        configurableConstants,
        abiInterface
      );
    }

    return {
      predicateBytes,
      predicateInterface: abiInterface,
    };
  }

View on GitHub (pinned to b3f37c91ac)

Solutions

1. Confirm the ABI is from a Sway predicate program (sway-project type 'predicate'), not a contract.
2. Open the ABI JSON and verify a top-level functions array contains an object with name: 'main'.
3. Recompile the predicate with forc build and ensure the entrypoint is declared as fn main() -> bool (or the SDK-expected signature).
4. Point the Predicate constructor at the correct abi JSON file generated alongside the predicate bytecode.

Example fix

// before — abi is a contract ABI with no main()
const predicate = new Predicate({ bytecode, abi: contractAbi });

// after — use the predicate's own ABI (has functions: [{ name: 'main', ... }])
const predicate = new Predicate({ bytecode, abi: predicateAbi });

function hasMainFunction(abi: { functions?: Array<{ name: string }> }): boolean {
  return Array.isArray(abi.functions) && abi.functions.some(f => f.name === 'main');
}
// call: if (!hasMainFunction(abi)) throw new Error('ABI must declare main() for a predicate');

function isPredicateAbi(abi: any): abi is { functions: Array<{ name: 'main' }> } {
  return Array.isArray(abi?.functions) && abi.functions.some((f: any) => f?.name === 'main');
}

import { FuelError, ErrorCode } from '@fuel-ts/errors';
try {
  const predicate = new Predicate({ bytecode, abi });
} catch (e) {
  if (e instanceof FuelError && e.code === ErrorCode.ABI_MAIN_METHOD_MISSING) {
    // load the predicate ABI instead of the contract ABI and retry
  }
  throw e;
}

When it happens

Trigger: Instantiating new Predicate({ abi, bytecode, ... }) where abi.functions has no 'main' entry; passing the ABI of a regular contract (which may have arbitrary function names) instead of a predicate ABI; passing an ABI from a Sway predicate compiled with a renamed main function; passing an empty or stub ABI.

Common situations: Building a Predicate from a contract ABI by mistake (contracts use arbitrary names, predicates use main); ABI file is from an older/different Sway compiler version that emitted a different entrypoint name; abi file path resolved to the wrong JSON; forja/typescript output mixed up between contract and predicate folders.

Related errors

• INVALID_CONFIGURABLE_CONSTANTS
• CONFIGURABLE_NOT_FOUND
• Data section offset is out of bounds, offset: ${offset}, bin
• TRANSACTION_ERROR
• INVALID_CONFIGURABLE_CONSTANTS

AI-assisted analysis of FuelLabs/fuels-ts@b3f37c91ac (2026-08-12). Data as JSON: /api/errors/a72dc24aab546921. Report an issue: GitHub.