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Nim implementation of the Ethereum 2.0 blockchain

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Nimbus Eth2 (Beacon Chain)

Build Status (Travis) Build Status (Azure) Github Actions CI License: Apache License: MIT Stability: experimental

Discord: Nimbus Status: #nimbus-general

Nimbus beacon chain is a research implementation of the beacon chain component of the upcoming Ethereum Serenity upgrade, aka Eth2.


You can find the information you need to run a beacon node and operate as a validator in The Book.

The Quickstart in particular will help you get connected to the Pyrmont Testnet and eth2 Mainnet quickly!

Related projects

You can check where the beacon chain fits in the Ethereum ecosystem our Two-Point-Oh series:

Branch guide

  • stable
    - latest stable release - this branch is recommended for most users
  • testing
    - pre-release branch with features and bugfixes slated for the next stable release - this branch is suitable for use on testnets and for adventerous users that want to live on the edge.
  • unstable
    - main development branch against which PR's are merged - if you want to contribute to Nimbus, start here.

Developer resources

To build tools that interact with Nimbus while it's running, we expose an RPC API.

To get started with developing Nimbus itself, see the developer handbook.

Nimbus is built in the Nim language - the compiler is automatically installed when building the project for the first time. More information - in particular security-related information about the language - can be found in the Auditor Handbook.

Interop tooling

After installing the prerequisites

We provide several tools to interact with ETH2:

  • ncli - command line tools to interact with blocks and states - pretty printers, SSZ decoders, state transition helpers
  • ncli_db - command line tool to perform surgery on the Nimbus sqlite database
  • inspector
  • multinet - a set of scripts to build and run several Eth2 clients locally

For researchers

State transition simulation

The state transition simulator can quickly run the Beacon chain state transition function in isolation and output JSON snapshots of the state. The simulation runs without networking and blocks are processed without slot time delays.

# build and run the state simulator, then display its help ("-d:release" speeds it
# up substantially, allowing the simulation of longer runs in reasonable time)
make NIMFLAGS="-d:release" state_sim
build/state_sim --help

Local network simulation

The local network simulation will create a full peer-to-peer network of beacon nodes and validators on a single machine, and run the beacon chain in real time.

Parameters such as shard, validator counts, and data folders are configured They can be set in as environment variables before launching the simulation.

# Clear data files from your last run and start the simulation with a new genesis block:
make VALIDATORS=192 NODES=6 USER_NODES=1 eth2_network_simulation

In another terminal, get a shell with the right environment variables set:

./ bash

In the above example, the network is prepared for 7 beacon nodes but one of

them is not started by default (USER_NODES) - this is useful to test

catching up to the consensus. The following command will start the missing node.

./tests/simulation/ 0 # (or the index (0-based) of the missing node)

Running a separate node allows you to test sync as well as see what the action

looks like from a single nodes' perspective.

By default, validators will be split in half between beacon node and validator client processes (50/50), communicating through the official validator API (for example with

validators and
nodes you will roughly end up with 6 beacon node and 6 validator client processes, where each of them will handle 16 validators), but if you don't want to use external validator clients and instead want to have all the validators handled by the beacon nodes you may use
as an additional argument to
make eth2_network_simulation

By default, the simulation will start from a pre-generated genesis state. If you wish to simulate the bootstrap process with a Ethereum 1.0 validator deposit contract, start the simulation with

make eth2_network_simulation WAIT_GENESIS=yes

You can also separate the output from each beacon node in its own panel, using multitail:

make eth2_network_simulation USE_MULTITAIL="yes"

You can find out more about it in the development update.

Alternatively, fire up our experimental Vagrant instance with Nim pre-installed and give us yout feedback about the process!

Visualising simulation metrics

The generic instructions from the Nimbus repo apply here as well.

Specific steps:

# This will generate the Prometheus config on the fly, based on the number of
# nodes (which you can control by passing something like NODES=6 to `make`).
# The `-d:insecure` flag starts an HTTP server from which the Prometheus daemon will pull the metrics.
make VALIDATORS=192 NODES=6 USER_NODES=0 NIMFLAGS="-d:insecure" eth2_network_simulation

In another terminal tab, after the sim started:

cd tests/simulation/prometheus prometheus

The dashboard you need to import in Grafana is "grafana/beacon_nodes_Grafana_dashboard.json".

monitoring dashboard

Network inspection

The inspector tool can help monitor the libp2p network and the various channels where blocks and attestations are being transmitted, showing message and connectivity metadata. By default, it will monitor all ethereum 2 gossip traffic.

. ./
# Build inspector for minimal config:
./ nim c -d:const_preset=minimal -o:build/inspector_minimal beacon_chain/inspector.nim

Build inspector for mainnet config:

./ nim c -d:const_preset=mainnet -o:build/inspector_mainnet beacon_chain/inspector.nim

See available options

./ build/inspector_minimal --help

Connect to a network from eth2 testnet repo bootstrap file - --decode option attempts to decode the messages as well

./ build/inspector_minimal --decode -b:$(curl -s | head -n1)

CI setup

Local testnets run for 4 epochs each, to test finalization. That happens only on Jenkins Linux hosts, and their logs are available for download as artifacts, from the job's page. Don't expect these artifacts to be kept more than a day after the corresponding branch is deleted.

Jenkins artifacts


Licensed and distributed under either of

  • MIT license: LICENSE-MIT or


  • Apache License, Version 2.0, (LICENSE-APACHEv2 or

at your option. These files may not be copied, modified, or distributed except according to those terms.

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