The Ethereum community has come up with different ERC (i.e., Ethereum Request for Comments) token standards (e.g., ERC-20, ERC-721, and ERC-1155) based on the different types of applications in the ecosystem. These are technical documents that specify essential aspects of a contract (management of transfers, delegation, etc.) for developers to adhere to when creating and deploying smart contracts in the Ethereum ecosystem. Contract developers should strive to follow the guidelines of ERC standards as they provide a reference frame during development.

But how confident can we be in the behavior of these contracts? Do they follow the standards? With the permissionless nature of blockchains, anyone can write and deploy smart contracts in blockchain ecosystems. However, smart contracts can be vulnerable to attacks especially in the DeFi space, e.g., the infamous DAO attack.

ERCx addresses these questions. ERCx is a platform that provides token investors, developers and auditors with independent and reliable information on the token properties. The rest of this page details this ambition and vision.


ERCx checks the conformance of a contract to ERC (Ethereum Request for Comments) standards. ERC standards exist for various sorts of tokens, fungible or not. ERC standards specify essential aspects of a contract (management of transfers, delegation, etc.). Contract developers should strive to follow the guidelines of ERC standards as they provide a reference frame during development.

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Conformance to the related ERC standard is a good indicator of the quality of a contract. While conformance does not constitute quality assurance, non-conformance indicates that something is wrong. But conformance does not suffice, important desirable properties should be respected as history showed that not respecting these leads to problems. ERCx aims at helping the Ethereum community by providing the following benefits to:

  • Contract Developers

    ERCx not only checks conformance before deployment (hence providing a sanity check) but also indicates satisfaction of important properties.

  • Token Investors

    Non-conformant contracts should be avoided at all costs. For token platforms, ERCx helps quickly assess the quality of some tokens.

  • Contract/Token Auditors

    ERCx provides a first round of assessment about the standard, allowing the expert review to focus on other potential bugs.


To check a given contract, ERCx uses property tests: for the contract under test (cut), we generate a tailored test suite, which is a collection of test cases. Each test case exercises one property prescribed by the underlying ERC standard. Our test suite relies on:

  1. property-based test cases that precisely test the expected behavior and provide user feedback in case of errors; our tests can also be tailored to users' needs, and
  2. the Foundry testing framework, a reliable and easy-to-setup tool that is widely used by developers and auditors.

By executing the ERCx test suite against a cut, we obtain a complete and precise diagnosis of the cut non-conformance or a conformance check. Passing (resp. failing) tests indicate that the contract respects (resp. violates) the associated property. For failing tests, we refer to the ERC standard, thus suggesting the required fixes. Overall, ERCx takes as input some contract description (which can be the source code, the deployment address or the bytecode, of the contract), generates and executes the tests, and finally produces a conformance report.

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Scope and Limitations

ERCx checks the contract using testing. While tests cover the whole ERC standard, they exercise only some part of the contract behavior. While our test suite should detect most of the main issues, it cannot detect tricky behavior that would be hidden inside the contract code. Contracts passing the test suite are not (necessarily) safe contracts! Moreover, if the contract has functions besides those described in the standard, they are ignored at the moment.

In addition to the above general scope, we are actively addressing the current following limitations:

  1. For some contracts such as Liquid staked Ether 2.0 (stETH), there are slight deviations in how they implemented some functions such astotalSupply() or balanceOf(address). Consequently, there could be some inaccessibility issues when looking for the right storage slots when testing properties. Thus, these contracts may fail tests from our test suite. Please exercise caution when interpreting test results.
  2. For some contracts such as Numeraire (NMR), they may fail all ABI tests with the error, reason: EvmError: OutOfGas, when you look under the “Detailed Report” tab. This is due to the test suite running out of gas while querying on their ABI contents. We will address this issue in our next update. Please ignore these ABI test results for the time being.
  3. If the provided address contains the token's proxy contract instead of its implementation contract, the test suite will fail all ABI tests. To get accurate results of the ABI tests for a token, please provide the address of its implementation contract.

Caution / Disclaimer
ERCx focuses on the technical aspect of a token. ERCx uses concrete testing over a finite set of input values and thus does not cover the full set of possible inputs. In particular, the results presented do not constitute financial analysis and should never be considered financial advice. The checks performed by ERCx do not constitute an audit.