A debugging tool that checks historical Arbitrum event responses against receipt evidence and produces reports other developers can verify offline and recheck later.
LogWitness helps Arbitrum application and indexer developers investigate missing, duplicated, reordered or altered blockchain events.
A developer supplies the historical eth_getLogs query they are investigating, an endpoint to check and a reference endpoint. LogWitness records the response, pins reference block headers, fetches transaction receipts and reconstructs supported Nitro receipt tries. It then compares the events in the verified receipts with the events returned by the endpoint.
The result is a portable .lw.json evidence bundle, a Markdown incident report and a local browser viewer. A maintainer can recompute the checks offline without access to the original application database or RPC credentials. LogWitness can also produce smaller supporting evidence and test whether a narrower query reproduces the discrepancy. The original incident is preserved, and a separate recheck command compares a later endpoint response against the saved reference.
The project includes EventProbe contracts deployed on Arbitrum Sepolia. Seven published test cases cover topic filters, multiple emitting addresses, repeated events, multiple logs, an empty result and a reverted transaction. These cases run through the same capture and verification pipeline as application queries.
The focus is the debugging handoff: giving a maintainer the query, evidence and instructions needed to investigate and retest a specific incident. Developers can use LogWitness alongside their existing RPC and indexing services.
Built the LogWitness MVP during the hackathon, including the CLI workflow for capturing and checking historical eth_getLogs responses, offline evidence verification, incident reduction, endpoint rechecking, Markdown reports, and a local viewer.
We also implemented and deployed the EventProbe test corpus on Arbitrum Sepolia, added live receipt acquisition with fallback handling, reconstructed supported Nitro receipt tries, and added automated tests for missing, duplicated, reordered, altered, incomplete, and tampered evidence cases. The repository also includes a real Arbitrum One capture, reproducible corpus cases, and a demo recording.
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