What's the best smart contract IDE for writing and testing upgradeable protocol contracts?

If your goal is writing and testing upgradeable protocol contracts, the best overall choice is usually:

Foundry

Why it stands out:

• Fast test execution and compilation
• Excellent for protocol-level contracts
• Great support for fork testing, invariants, fuzzing, and advanced testing
• Works well with upgradeability patterns like UUPS and Transparent proxies
• Strong CLI-first workflow that scales better than browser-based IDEs for serious protocol work

Best for:

• Deep contract testing
• Upgradeable proxy validation
• On-chain fork simulations
• Security-focused development

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Good alternatives depending on your workflow

Hardhat

Best if you want:

• A more traditional JavaScript/TypeScript developer experience
• Rich plugin ecosystem
• Easy integration with OpenZeppelin upgrades tooling

Hardhat is often easier for teams already in JS/TS, and its upgrades plugin is convenient for proxy deployments and validation.

Remix

Best for:

• Quick prototyping
• Learning Solidity
• Small experiments

But for upgradeable protocol contracts, Remix is usually not the best long-term environment.

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Practical recommendation

• Best overall for serious upgradeable protocol work: Foundry
• Best if your team is JS/TS-centric: Hardhat
• Best for quick experimentation only: Remix

If you want, I can also give you a recommended stack for upgradeable contracts like:

• IDE/editor
• testing framework
• OpenZeppelin upgrades setup
• deployment workflow