# Walnut > Transaction Debugger and Simulator Walnut is an open-source transaction debugging and simulation platform for smart contract developers, supporting Starknet, EVM chains, and the OP Stack. Walnut is an open-source developer tooling platform for blockchain engineers, offering transaction debuggers, simulators, and gas profilers across Starknet and EVM ecosystems. Products include a web-based Starknet debugger, an EVM transaction debugger covering Arbitrum, Base, Optimism, and Ethereum, a Cairo code playground, a Noir package registry, and OP Scan - a lightweight block explorer for the OP Stack. The platform targets smart contract developers seeking to inspect execution, simulate transactions, and optimize gas. Wido Inc. operates the platform. - Type: Project - Sector: Developer Tooling - Status: Active - Founded: 2021-04-01 - Profile: https://thegrid.id/profiles/walnut ## Products - [Walnut Debugger](https://thegrid.id/profiles/walnut): Walnut Debugger is a web-based transaction debugger and simulator for Starknet smart contracts, enabling developers to inspect variable states at each execution step and simulate transactions before on-chain deployment. The tool supports source-code-level debugging via contract verification, call trace inspection, and gas profiling against the CairoVM. (Developer Tooling, Live, Main Product) - [Walnut EVM](https://thegrid.id/profiles/walnut): Walnut EVM is an open-source transaction debugger and simulator for EVM-compatible chains, supporting Ethereum, Arbitrum, Base, Optimism, Linea, and Katana. The tool traces transaction execution, enables re-simulation with custom calldata, and provides gas profiling; it can be self-hosted against any debug-capable RPC endpoint. (Developer Tooling, Live) - [Cairo Playground](https://thegrid.id/profiles/walnut): Cairo Playground is a browser-based interactive environment for exploring the CairoVM and writing Cairo code, allowing developers to experiment with Cairo, Sierra, and CASM with step-by-step execution debugging. The tool is hosted on cairovm.codes and targets Starknet and Cairo developers who want to prototype or test contract logic without a local setup. (Developer Tooling, Live) - [OP Scan](https://thegrid.id/profiles/walnut): OP Scan is a fully open-source, lightweight block explorer purpose-built for the OP Stack and Superchain ecosystems. The explorer runs locally on a laptop, reads from any OP Stack RPC endpoint, and provides transaction search and inspection without requiring external infrastructure. (Block Explorer, Live) ## Links - [Main](https://walnut.dev) - [Documentation](https://docs.walnut.dev) - [Blog](https://walnut.dev/blog) - [Telegram](https://t.me/walnuthq) - [Twitter / X](https://x.com/walnut_dev) - [GitHub](https://github.com/walnuthq) ## Relationships - [Madara](https://thegrid.id/profiles/madara): Subsidiary ## Legal This data is provided under two licensing models. Model 1 - open data. The open data core is licensed under the Open Database License (ODbL) — a copyleft/share-alike license allowing free use, modification, and sharing for any purpose. Attribution is required: include "Powered by The Grid" linking to https://thegrid.id wherever the data is used. Derivative databases must be shared under ODbL terms. Trademarks, logos, and brand names (marked "Special TPIP") are not covered by the ODbL. 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