Top 6 Developer-Focused Debugging Tools (Tenderly, Moralis-style) That Smart Contract Engineers Use to Replay Transactions and Prevent Failures

Debugging smart contracts is one of the most critical tasks in blockchain development. Whether it’s monitoring gas costs, identifying edge case failures, or ensuring that a DeFi protocol functions as intended, developers rely heavily on debugging tools that allow them to replay, inspect, and analyze transactions in granular detail. With the increasing complexity of decentralized applications (dApps), having access to developer-friendly debugging environments is no longer optional—it’s essential.

TL;DR

If you’re developing smart contracts, leveraging tools that replay on-chain transactions and uncover hidden bugs is crucial. Top debugging platforms like Tenderly and Moralis bring real-time analytics and automated debugging functions that boost developer productivity and confidence. The list below covers six leading solutions that help engineers prevent failures and streamline smart contract testing. From deep EVM tracing to mainnet forking, these tools make Web3 debugging intuitive and reliable.

1. Tenderly: Comprehensive Transaction Replayer and Debugger

Tenderly is widely regarded as a powerhouse debugging suite tailored specifically for smart contract developers. Its seamless integration with Ethereum Virtual Machine (EVM)-compatible chains allows engineers to recreate failed transactions instantly using the Transaction Simulator.

Some standout features include:

• Transaction Replays: Re-execute any on-chain transaction and inspect the changes in real-time.
• Gas Profiler: Optimize gas usage by analyzing each operation’s cost.
• State Inspector: View variable-level changes throughout the contract execution flow.
• Custom Events Monitoring: Get notified when specific contract functions or failures occur.

Tenderly is especially helpful when testing contract upgrades on forked mainnets, bridging CI/CD practices to decentralized code deployment. Its no-code dashboard is perfect for developers who want in-depth insight without requiring additional configuration.

2. Moralis: Full-Stack Web3 Debugging and Observability

Moralis is known for its robust backend-as-a-service suite—but many developers overlook its value as a debugging platform. For smart contract engineers, Moralis brings a powerful transaction monitoring system combined with node-level tracing capabilities.

Moralis offers:

• Live Transaction Listener: Instantly fetch and analyze real-time and historical on-chain data.
• Manual Replay Functionality: Re-trigger transactions in local or testchain environments.
• Integrated Logs & Breakpoints: Dissect workflows from frontend APIs to blockchain execution.

It’s ideal for full-stack dApp developers who want to debug both the smart contract logic and the surrounding infrastructure like user authentication, database sync, and wallet-triggered events.

3. Foundry: Advanced Local Mainnet Forking for Solidity Developers

Foundry is a blazing fast smart contract development toolkit written in Rust, making it ideal for EVM developers who value speed and precision. Its most powerful feature is the ability to fork the mainnet directly into a local test environment at any given block number.

With Foundry, engineers can:

• Replay Transactions from known blockchains using forked state.
• Inject altered variables to simulate new behaviors and test edge-case scenarios.
• Use built-in fuzz testing and symbolic execution to auto-detect risky code paths.

Foundry’s CLI-first architecture is highly customizable and integrates seamlessly with CI pipelines or EVM-based Layer 2 testnets.

4. Hardhat: Versatile Testing and Debugging Framework

Hardhat is one of the most popular smart contract frameworks thanks to its extensibility and support for plugin development. With tools like hardhat-network, developers can simulate a full Ethereum environment locally and experiment with contract interactions in real-time.

Debugging-related features include:

• Stack Tracing: Read human-readable traces of failed transactions with exact line references.
• Network Forking: Replay specific on-chain calls from any block.
• Console Logs: Debug contracts mid-execution using Solidity console statements.

Hardhat is particularly useful during development sprints when iteration speed matters. Its tight integration with Mocha and Chai testing libraries makes it a great all-in-one debugging and testing toolkit.

5. Remix IDE: Beginner-Friendly Debugger with Visual Insight

Remix IDE may be browser-based, but it’s more than capable of handling robust smart contract debugging. Its visual debugger gives an intuitive step-by-step walk-through of contract execution, making it the ideal tool for new developers or educators.

What Remix offers:

• Step-Through Debugger: Watch EVM opcode execution live, with variable value updates.
• Storage View: Inspect how storage changes line-by-line through execution.
• Breakpoints and Watch Expressions: Set and monitor variable values to catch errors early.

While not ideal for replaying live mainnet transactions, Remix excels in isolated debugging sessions—when reviewing contract failures or testing hypotheticals based on code rather than state.

6. Sentio: Observability Platform for Live Smart Contract Monitoring

Sentio is a rising star in the Web3 observability space. While not strictly a transaction replayer, it offers infrastructure that complements debugging tools by tracking live execution events, anomalies, and performance metrics.

Sentio focuses on:

• Realtime Event Tracking: Collect custom contract events in Prometheus-style metrics streams.
• Error Frequency Alerts: Trigger automated alerts when failure patterns appear.
• Graph-Based Call Analysis: Visualize how different contracts interact during execution.

Used in conjunction with tools like Tenderly or Hardhat, Sentio provides valuable production-level insights that aid in retrospective debugging and dynamic code health monitoring.

Conclusion

Smart contract development demands a blend of precision, foresight, and real-time analytics. The tools listed here—Tenderly, Moralis, Foundry, Hardhat, Remix, and Sentio—equip developers with everything they need to debug effectively, replay crucial transactions, and optimize smart contract workflows. Choosing the right tool depends on your scope: whether you’re forking mainnet states, monitoring deployed contracts, or debugging pre-deployment logic, there’s a solution tailored for each stage in the dApp lifecycle.

FAQ

• Q: What does “replaying a transaction” mean in smart contract development?
  A: Replaying a transaction means executing a previously sent transaction under the same or altered conditions to debug execution paths or verify behavior in a controlled environment.
• Q: Why is mainnet forking useful for debugging?
  A: Forking creates a local copy of the blockchain at a specific point in time, enabling developers to test their contracts with real-world data, token balances, and contract interactions without affecting the live network.
• Q: How do Tenderly and Moralis differ for debugging?
  A: Tenderly focuses primarily on deep EVM-based debugging, simulation, and error analysis, while Moralis provides a broader full-stack environment with tools for monitoring wallet actions, backend logs, and application-side debugging.
• Q: Can these tools be used together in a workflow?
  A: Absolutely. For example, developers might deploy contracts using Hardhat, replay bugs using Tenderly, and monitor them live on Sentio for error patterns—creating a full lifecycle debugging pipeline.
• Q: Which tool is best for debugging a failed DeFi trade?
  A: Tenderly or Foundry are best suited since they allow deep inspection of transaction state, internal calls, and revert reasons affecting complex token swaps or lending protocols.