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Celo Blockchain

Official golang implementation of the Celo blockchain, based off of the official golang implementation of the Ethereum protocol.

CircleCI Codecov Discord

Prebuilt Docker images are available for immediate use: See for a guide to the Celo networks and how to get started.

Documentation for Celo more generally can be found at

Most functionality of this client is similar to go-ethereum, also known as geth, from which it was forked. If you do not find your question answered by Celo-specific documentation, try searching the geth wiki.

Building the source

Building geth requires both Go (min version 1.19) and a C compiler. You can install them using your favourite package manager. Once the dependencies are installed, run

make geth

or, to build the full suite of utilities:

make all

Mobile Clients

There are two different commands in the Makefile to build the ios and the android clients.

make ios


make android

Note: The android command it applies a git patch (patches/mobileLibsForBuild.patch) required to swap some libs from the go.mod for the client to work, installs those libs, builds the client, and then reverts the patch.


The Celo blockchain client comes with several wrappers/executables found in the cmd directory.

Command Description
geth The main Celo Blockchain client. It is the entry point into the Celo network, capable of running as a full node (default), archive node (retaining all historical state), light node (retrieving data live), or lightest node (retrieving minimum number of block headers to verify existing validator set). It can be used by other processes as a gateway into the Celo network via JSON RPC endpoints exposed on top of HTTP, WebSocket and/or IPC transports. geth --help and the Ethereum CLI Wiki page for command line options.
abigen Source code generator to convert Celo contract definitions into easy to use, compile-time type-safe Go packages. It operates on plain Ethereum contract ABIs with expanded functionality if the contract bytecode is also available. However it also accepts Solidity source files, making development much more streamlined. Please see Ethereum's Native DApps wiki page for details.
bootnode Stripped down version of the Celo client implementation that only takes part in the network node discovery protocol, but does not run any of the higher level application protocols. It can be used as a lightweight bootstrap node to aid in finding peers in private networks.
evm Developer utility version of the EVM (Ethereum Virtual Machine) that is capable of running bytecode snippets within a configurable environment and execution mode. Its purpose is to allow isolated, fine-grained debugging of EVM opcodes (e.g. evm --code 60ff60ff --debug run).
gethrpctest Developer utility tool to support the ethereum/rpc-test test suite which validates baseline conformity to the Ethereum JSON RPC specs. Please see the ethereum test suite's readme for details.
rlpdump Developer utility tool to convert binary RLP (Recursive Length Prefix) dumps (data encoding used by the Celo protocol both network as well as consensus wise) to user friendlier hierarchical representation (e.g. rlpdump --hex CE0183FFFFFFC4C304050583616263).

Running tests

Prior to running tests you will need to run make prepare, this will run two sub rules.

Without first running this make prepare, certain tests will fail.


This will shallow checkout the celo-monorepo under ../.celo-blockchain-monorepo-checkout relative to this project's root at the commit defined in the file monorepo_commit. Then it will compile the system contracts for use in full network tests. The rule will copy the compiled contracts from celo-monorepo to compiled-system-contracts. If you subsequently edit the system contracts source or monorepo_commit, running the make rule again will re-checkout the monorepo, re-compile the contracts and copy them into place.

monorepo_commit may contain a commit hash or a tag, branch names are forbidden.

In the case that you would like to change the default monorepo checkout location, or that you would like to have multiple checkouts of the monorepo (at different versions) you can set the MONOREPO_PATH variable in the make command, for example:

make prepare-system-contracts MONOREPO_PATH=../alt-monorepo

Note that MONOREPO_PATH should not be set to point at checkouts other than those checked out by the prepare-system-contracts rule, and the checkouts created by the prepare-system-contracts rule should not be manually modified, aside from changing the contract source.


This will install dependencies for the ethersjs-api-check typescript project.

Running Celo

Please see the for instructions on how to run a node connected to the Celo network using the prebuilt Docker image.

Going through all the possible command line flags is out of scope here, please consult geth --help for more complete information. We've enumerated a few common parameter combos to get you up to speed quickly on how you can run your own Celo blockchain client instance.

Full node on the main Celo network

By default, the Celo client will connect to the Mainnet. Running the following command will create a full node that will sync with the Celo network and allow access to all of its functionality.

$ geth console

This command will:

  • Start geth in full sync mode which will download and execute all historical block information.
  • Start up geth's built-in interactive JavaScript console, (via the trailing console subcommand) through which you can invoke all official web3 methods as well as geth's own management APIs. This tool is optional and if you leave it out you can always attach to an already running geth instance with geth attach.

A Full node on the Alfajores test network

Smart contract developers will be most interested in the Alfajores testnet. On Alfajores, you can receive testnet Celo through the Alfajores faucet and deploy smart contracts in an environment very similar to Mainnet. More information about the Alfajores testnet can be found on

$ geth --alfajores console

Note: Although there are some internal protective measures to prevent transactions from crossing over between the main network and test network, you should make sure to always use separate accounts for testnet-tokens and real-tokens. Unless you manually move accounts, geth will by default correctly separate the two networks and will not make any accounts available between them.

Full node on the Baklava test network

Validators and full node operators will be most interested in the Baklava testnet. On Baklava, you can receive a distribution of testnet Celo Gold to become a validator on the network and test out running a validator for the first time, or try out new infrastructure. More information about the Baklava testnet can be found on A full guide to getting started as a validator on Baklava can be found in the Getting Started guides

$ geth --baklava console


As an alternative to passing the numerous flags to the Celo binary, you can also pass a configuration file via:

$ geth --config /path/to/your_config.toml

To get an idea of how the file should look like you can use the dumpconfig subcommand to export your existing configuration:

$ geth --your-favourite-flags dumpconfig

Programmatically interfacing geth nodes

As a developer, sooner rather than later you'll want to start interacting with geth and the Celo network via your own programs and not manually through the console. To aid this, geth has built-in support for a JSON-RPC based APIs (standard APIs and geth specific APIs). These can be exposed via HTTP, WebSockets and IPC (UNIX sockets on UNIX based platforms, and named pipes on Windows).

The IPC interface is enabled by default and exposes all the APIs supported by geth, whereas the HTTP and WS interfaces need to manually be enabled and only expose a subset of APIs due to security reasons. These can be turned on/off and configured as you'd expect.

HTTP based JSON-RPC API options:

  • --http Enable the HTTP-RPC server
  • --http.addr HTTP-RPC server listening interface (default: localhost)
  • --http.port HTTP-RPC server listening port (default: 8545)
  • --http.api API's offered over the HTTP-RPC interface (default: eth,net,web3)
  • --http.corsdomain Comma separated list of domains from which to accept cross origin requests (browser enforced)
  • --ws Enable the WS-RPC server
  • --ws.addr WS-RPC server listening interface (default: localhost)
  • --ws.port WS-RPC server listening port (default: 8546)
  • --ws.api API's offered over the WS-RPC interface (default: eth,net,web3)
  • value Origins from which to accept websockets requests
  • --graphql Enable GraphQL on the HTTP-RPC server. Note that GraphQL can only be started if an HTTP server is started as well.
  • --graphql.corsdomain value Comma separated list of domains from which to accept cross origin requests (browser enforced)
  • --graphql.vhosts value Comma separated list of virtual hostnames from which to accept requests (server enforced). Accepts '*' wildcard. (default: "localhost")
  • --ipcdisable Disable the IPC-RPC server
  • --ipcapi API's offered over the IPC-RPC interface (default: admin,debug,eth,miner,net,personal,shh,txpool,web3)
  • --ipcpath Filename for IPC socket/pipe within the datadir (explicit paths escape it)

You'll need to use your own programming environments' capabilities (libraries, tools, etc) to connect via HTTP, WS or IPC to a geth node configured with the above flags and you'll need to speak JSON-RPC on all transports. You can reuse the same connection for multiple requests!

Note: Please understand the security implications of opening up an HTTP/WS based transport before doing so! Hackers on the internet are actively trying to subvert Celo nodes with exposed APIs! Further, all browser tabs can access locally running web servers, so malicious web pages could try to subvert locally available APIs!


Thank you for considering to help out with the source code! We welcome contributions from anyone on the internet, and are grateful for even the smallest of fixes!

If you'd like to contribute to celo-blockchain, please fork, fix, commit and send a pull request for the maintainers to review and merge into the main code base. If you wish to submit more complex changes though, please check up with the core devs first on the official Celo forum to ensure those changes are in line with the general philosophy of the project and/or get some early feedback which can make both your efforts much lighter as well as our review and merge procedures quick and simple.

Please make sure your contributions adhere to our coding guidelines:

  • Code must adhere to the official Go formatting guidelines (i.e. uses gofmt).
  • Code must be documented adhering to the official Go commentary guidelines.
  • Pull requests need to be based on and opened against the master branch.
  • Commit messages should be prefixed with the package(s) they modify.
    • E.g. "eth, rpc: make trace configs optional"

Submitting an issue

If you come across a bug, please open a GitHub issue with information about your build and what happened.

CI Testing and automerge

We run a circle CI test suite on each PR. The following tests are required to merge a PR.

  • Unit tests: make test or ./build/ go run build/ci.go test
  • Lint: make lint (Fix go format errors with gofmt -s)
  • Build: make
  • End to end sync and transfer tests
  • Check imports: ./scripts/

celo-blockchain is based on go-ethereum, but the import path has been renamed from to Developers are encouraged to run ./scripts/ to enable checking that import path has been changed to celo-org on git merge and git commit. Imports can automatically be renamed with ./scripts/

Individual package tests can be run with ./build/ go test$(PATH_TO_GO_PACKAGE) if you don't have GOPATH set-up.

Once a PR is approved, adding on the automerge label will keep it up to date and do a squash merge once all the required tests have passed.


Golang has built-in support for running benchmarks with go tool go test -run=ThisIsNotATestName -bench=. ./$PACKAGE_NAME will run all benchmarks in a package.

One note around running benchmarks is that BenchmarkHandlePreprepare is quite takes a while to run, particularly when testing with a larger number of validators. Substituting -bench=REGEX for -bench=. will specify which tests to run. Adding -cpuprofile=cpu.out which can be visualized with go tool pprof -html:8080 cpu.out if graphviz is installed.

See the go testing flags and go docs for more information on benchmarking.


The celo-blockchain library (i.e. all code outside of the cmd directory) is licensed under the GNU Lesser General Public License v3.0, also included in our repository in the COPYING.LESSER file.

The celo-blockchain binaries (i.e. all code inside of the cmd directory) is licensed under the GNU General Public License v3.0, also included in our repository in the COPYING file.