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Flow Emulator

The Flow Emulator is a lightweight tool that emulates the behavior of the real Flow network for local development and testing.

Installation​

The emulator is included with the Flow CLI. Follow the installation guide to get started.

Quick Start​

First, create a flow.json configuration file:


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flow init --config-only

Then start the Flow Emulator:


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flow emulator

This starts a local Flow network with:

  • gRPC server on port 3569
  • REST API on http://localhost:8888
  • Admin API on port 8080

Common Options​


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# Start with verbose logging
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flow emulator --verbose
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# Set custom block time (e.g., 1 second between blocks)
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flow emulator --block-time 1s
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# Persist state between restarts
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flow emulator --persist

For all available options, see the CLI commands overview.

Debugging & Testing​

  • Code Coverage: Add --coverage-reporting flag and visit http://localhost:8080/emulator/codeCoverage
  • Debugging: Use #debugger() pragma in Cadence code for breakpoints

Additional Resources​

For advanced configuration options, see the Flow Emulator repository.

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