The debug and trace APIs are used by developers to debug and analyze smart contracts and transactions. The debug API allows for code execution simulation, while the trace API traces contract execution and gathers data on various performance metrics.

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Developers can access the debug and trace tools on the Ethereum blockchain with the following methods:

• debug_traceBlockByHash
• debug_traceBlockByNumber
• debug_traceTransaction
• debug_traceCall
• trace_transaction
• trace_block

Pre-built JavaScript-based tracers

Developers can customize the type of tracing using various debug and trace methods, and there are numerous pre-built tracers available to choose from. Here is a list of the pre-built tracers that can be utilized:

4byteTracer

This tracer looks for function signatures that are 4 bytes long during contract execution and gathers information about the method identifiers and the size of the provided data. This information can be helpful in matching a signature against the data size.

bigramTracer

This tracer extracts bigram opcodes, which are pairs of adjacent opcodes, which means opcodes executed in sequence one after the other, and can provide insight into the control flow of a contract's execution.

callTracer

This tracer extracts information about all internal calls made by a transaction, providing visibility into how contracts interact with each other.

evmdisTracer

This tracer returns sufficient information from a trace to perform evmdis-style disassembly, which can be useful for reverse engineering contracts and identifying vulnerabilities.

opcountTracer

This tracer returns the number of instructions executed by the Ethereum Virtual Machine before the transaction is terminated.

prestateTracer

This tracer returns sufficient information about an account to create a local execution of the transaction. This procedure runs the given transaction again and monitors every aspect of the state that is modified or accessed during execution.

trigramTracer

This tracer extracts trigram opcodes, which are sets of three adjacent opcodes, and reports how many times each of these combinations is observed during contract execution.

unigramTracer

This tracer extracts individual opcodes and returns how many times each opcode was executed, which can be useful for analyzing the behavior of specific instructions in a contract.

Custom JavaScript tracers

JavaScript-based tracers can be created through various approaches, allowing them to interact with transaction information in diverse ways. By providing a JavaScript formula along with the tracking option when employing any of the available tracking techniques, users can craft tailor-made trackers to suit their specific requirements.

Find a guide to Custom JS tracing | Ethereum on the next page.