Skip to main content

FAQs

This page answers common questions encountered by developers building applications on Flare networks.

Technical Troubleshooting​

Why am I getting invalid opcode: opcode 0x5f not defined when deploying or interacting with my contract?​

Cause: This error typically occurs because your contract was compiled with a Solidity version (usually >=0.8.20) that defaults to the shanghai EVM version (or later), which introduced the PUSH0 (0x5f) opcode. Flare and Songbird currently support EVM versions up to london, which does not recognize this opcode.

Solution: You need to explicitly tell your compiler to target the london EVM version.

  • Using Remix: Set EVM version to london in the Advanced Configurations section of the Solidity Compiler tab:

  • Using Hardhat: Set evmVersion: "london" within the solidity configuration object in your hardhat.config.ts (or .js):

    // hardhat.config.ts
    import { HardhatUserConfig } from "hardhat/config";
    // ... other imports

    const config: HardhatUserConfig = {
      solidity: {
        version: "0.8.24", // Example version
        settings: {
          optimizer: {
            enabled: true,
            runs: 200,
          },
          evmVersion: "london", // Add this line
        },
      },
      // ... other configurations
    };

    export default config;

    See the Hardhat Starter Kit config for a full example.

  • Using Foundry: Add evm_version = "london" under the [profile.default] section in your foundry.toml:

    # foundry.toml
    [profile.default]
    src = "src"
    out = "out"
    libs = ["lib"]
    # ... other settings
    evm_version = "london" # Add this line

    See the Foundry Starter Kit config for a full example.

  • Using Standard Solidity JSON Input: Set evmVersion to london within the settings object:

    {
      "language": "Solidity",
      "sources": {
        /* ... */
      },
      "settings": {
        "optimizer": {
          /* ... */
        },
        "evmVersion": "london", // Set this
        "outputSelection": {
          /* ... */
        }
      }
    }

  • Using solc CLI: Use the --evm-version london flag:

    solc --evm-version london --optimize --abi --bin YourContract.sol -o build/

Network & Tokens​

Where can I get testnet tokens (faucet)?​

Flare provides faucets for its public testnets:

  • Flare Testnet Coston2: Get C2FLR from the Coston2 Faucet. Use Coston2 for testing applications intended for Flare mainnet.
  • Songbird Testnet Coston: Get CFLR from the Coston Faucet. Use Coston for testing applications intended for the Songbird canary network.

How do I add Flare/Songbird networks to my wallet (e.g., MetaMask)?​

The easiest way is to visit the respective block explorer, scroll down to the footer, and click the "Add Network" button:

Alternatively, you can add them manually using the details on the Network Configuration page.

What's the difference between Flare and Songbird?​

  • Flare (FLR): The main production network with real economic value.
  • Songbird (SGB): A "canary network" - blockchain used for testing protocol-level features and dApps in a live environment with real consequences before they are potentially deployed to Flare. It serves as a proving ground.

Read more on the Network Overview page.

Which RPC endpoint should I use?​

  • For Development/Testing: The Public RPCs are convenient for getting started. However, they have rate limits and shared resources.
  • For Production Applications: It is strongly recommended to use a dedicated RPC endpoint from a provider for better performance, reliability, and support. See the Developer Tools page for options.
  • For Running Nodes: You can also run your own RPC node.

What is the block time and finality on Flare?​

Flare networks use the Snowman++ consensus protocol.

  • Block Time: Approximately 1.8 seconds.
  • Finality: Near-instantaneous (single-slot finality). Once a block is accepted by consensus, it's considered final.

Learn more on the Consensus page.

Development Resources​

Where can I find the addresses of Flare's core smart contracts?​

The addresses for contracts like WNat, FtsoV2, FdcHub, etc., vary by network.

  1. Use the FlareContractRegistry: This contract acts as a directory. It has the same address (0xaD67FE66660Fb8dFE9d6b1b4240d8650e30F6019) on all Flare networks (Flare, Coston2, Songbird, Coston). You can query its getContractAddressByName or getAllContracts methods to find the addresses of other contracts on the specific network you are connected to.
  2. Check the Solidity Reference: Deployed contract addresses for each network are listed on the relevant reference pages for convenience:

Are there official developer tools or SDKs?​

Flare maintains several resources to aid development:

Where can I learn about Flare-specific terminology?​

Learn more about the terminology used in the Flare ecosystem (like FTSO, FSP, PDA, etc.) on the Terminology page.

Community & Support​

I have a project I would like to build on Flare. Can I get a grant?​

Yes! The Flare Foundation offers grants to support innovative projects that contribute to the ecosystem's growth. Learn more and apply on the Flare Grants Program page.

Where can I get technical support or ask questions?​

Connect with Flare's developer community and the team through these channels:

  • Flare Experts: Get dedicated Developer Support from a Flare expert.
  • Discord: The primary channel for developer Q&A, discussions, and support. Join the Flare Network Discord and head to the developer channels.
  • Telegram: Engage with the broader community on Telegram (may be less developer-focused).
  • GitHub: Report issues, contribute to code, or explore the open-source repositories at Flare Foundation GitHub. (Best for code-specific issues, not general Q&A).