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Stacks 2.0

Reference implementation of the Stacks blockchain in Rust.

Stacks 2.0 is a layer-1 blockchain that connects to Bitcoin for security and enables decentralized apps and predictable smart contracts. Stacks 2.0 implements Proof of Transfer (PoX) mining that anchors to Bitcoin security. Leader election happens at the Bitcoin blockchain and Stacks (STX) miners write new blocks on the separate Stacks blockchain. With PoX there is no need to modify Bitcoin to enable smart contracts and apps around it. See this page for more details and resources.



Blockstack Topic/Tech Where to learn more more
Stacks 2.0 master branch
Stacks 1.0 legacy branch
Use the package our core docs
Develop a Blockstack App our developer docs
Use a Blockstack App our browser docs
Blockstack PBC the company our website

Release Schedule and Hotfixes

Normal releases in this repository that add features such as improved RPC endpoints, improved boot-up time, new event observer fields or event types, etc., are released on a monthly schedule. The currently staged changes for such releases are in the develop branch. It is generally safe to run a stacks-node from that branch, though it has received less rigorous testing than release tags. If bugs are found in the develop branch, please do report them as issues on this repository.

For fixes that impact the correct functioning or liveness of the network, hotfixes may be issued. These are patches to the main branch which are backported to the develop branch after merging. These hotfixes are categorized by priority according to the following rubric:

  • High Priority. Any fix for an issue that could deny service to the network as a whole, e.g., an issue where a particular kind of invalid transaction would cause nodes to stop processing requests or shut down unintentionally. Any fix for an issue that could cause honest miners to produce invalid blocks.
  • Medium Priority. Any fix for an issue that could cause miners to waste funds
  • Low Priority. Any fix for an issue that could deny service to individual nodes


This repository uses a 5 part version number.


X = 2 and does not change in practice unless there’s another Stacks 2.0 type event
Y increments on consensus-breaking changes
Z increments on non-consensus-breaking changes that require a fresh chainstate (akin to semantic MAJOR)
A increments on non-consensus-breaking changes that do not require a fresh chainstate, but introduce new features (akin to semantic MINOR)
n increments on patches and hot-fixes (akin to semantic PATCH)

For example, a node operator running version would not need to wipe and refresh their chainstate to upgrade to or However, upgrading to would require a new chainstate.


Stacks improvement proposals (SIPs) are aimed at describing the implementation of the Stacks blockchain, as well as proposing improvements. They should contain concise technical specifications of features or standards and the rationale behind it. SIPs are intended to be the primary medium for proposing new features, for collecting community input on a system-wide issue, and for documenting design decisions.

See SIP 000 for more details.

The SIPs are now located in the stacksgov/sips repository as part of the Stacks Community Governance organization.

Testnet versions

  • Helium is a developer local setup, mono-node, assembling SIP 001, SIP 002, SIP 004 and SIP 005. With this version, developers can not only run Stacks 2.0 on their development machines, but also write, execute, and test smart contracts. See the instructions below for more details.

  • Neon is the first version of our public testnet, which shipped in Q2 2020. This testnet added SIP 003, and will be an open-membership public network, where participants will be able to validate and participate in mining testnet blocks.

  • Argon is the second version of our public testnet, which shipped in Q2 2020. This testnet improved on the stability of the Neon testnet.

  • Krypton is the third version of our public testnet, which incorporates a partial implementation of SIP 007. It allows developers to test a simple version of Stacking and PoX consensus.

  • Xenon is the upcoming version of our public testnet, which will run on the Bitcoin testnet. It will include SIP 006 and SIP 008, and will contain bugfixes and improvements to the implementation of SIP 007.

  • Mainnet is the fully functional version, that is estimated for Q4 2020.

See the testnet website and "when mainnet?" FAQ for details.

Getting started

Download and build stacks-blockchain

The first step is to ensure that you have Rust and the support software installed.

curl --proto '=https' --tlsv1.2 -sSf | sh

For building on Windows, follow the rustup installer instructions at

From there, you can clone this repository:

git clone --depth=1

cd stacks-blockchain

Then build the project:

cargo build

Run the tests:

cargo test testnet  -- --test-threads=1

Encode and sign transactions

Here, we have generated a keypair that will be used for signing the upcoming transactions:

cargo run --bin blockstack-cli generate-sk --testnet

# Output
# {
#  secretKey: "b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001",
#  publicKey: "02781d2d3a545afdb7f6013a8241b9e400475397516a0d0f76863c6742210539b5",
#  stacksAddress: "ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH"
# }

This keypair is already registered in the testnet-follower-conf.toml file, so it can be used as presented here.

We will interact with the following simple contract kv-store. In our examples, we will assume this contract is saved to ./kv-store.clar:

(define-map store { key: (string-ascii 32) } { value: (string-ascii 32) })

(define-public (get-value (key (string-ascii 32)))
    (match (map-get? store { key: key })
        entry (ok (get value entry))
        (err 0)))

(define-public (set-value (key (string-ascii 32)) (value (string-ascii 32)))
        (map-set store { key: key } { value: value })
        (ok true)))

We want to publish this contract on chain, then issue some transactions that interact with it by setting some keys and getting some values, so we can observe read and writes.

Our first step is to generate and sign, using your private key, the transaction that will publish the contract kv-store. To do that, we will use the subcommand:

cargo run --bin blockstack-cli publish --help

With the following arguments:

cargo run --bin blockstack-cli publish b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 515 0 kv-store ./kv-store.clar --testnet

The 515 is the transaction fee, denominated in microSTX. Right now, the testnet requires one microSTX per byte minimum, and this transaction should be less than 515 bytes. The third argument 0 is a nonce, that must be increased monotonically with each new transaction.

This command will output the binary format of the transaction. In our case, we want to pipe this output and dump it to a file that will be used later in this tutorial.

cargo run --bin blockstack-cli publish b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 515 0 kv-store ./kv-store.clar --testnet | xxd -r -p > tx1.bin

Run the testnet

You can observe the state machine in action locally by running:

cargo testnet start --config=./testnet/stacks-node/conf/testnet-follower-conf.toml

testnet-follower-conf.toml is a configuration file that you can use for setting genesis balances or configuring Event observers. You can grant an address an initial account balance by adding the following entries:

amount = 100000000

The address field is the Stacks testnet address, and the amount field is the number of microSTX to grant to it in the genesis block. The addresses of the private keys used in the tutorial below are already added.

Publish your contract

Assuming that the testnet is running, we can publish our kv-store contract.

In another terminal (or file explorer), you can move the tx1.bin generated earlier, to the mempool:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx1.bin http://localhost:20443/v2/transactions

In the terminal window running the testnet, you can observe the state machine's reactions.

Reading from / Writing to the contract

Now that our contract has been published on chain, let's try to submit some read / write transactions. We will start by trying to read the value associated with the key foo.

To do that, we will use the subcommand:

cargo run --bin blockstack-cli contract-call --help

With the following arguments:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 1 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store get-value -e \"foo\" --testnet | xxd -r -p > tx2.bin

contract-call generates and signs a contract-call transaction.

We can submit the transaction by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx2.bin http://localhost:20443/v2/transactions

Similarly, we can generate a transaction that would be setting the key foo to the value bar:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 2 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store set-value -e \"foo\" -e \"bar\" --testnet | xxd -r -p > tx3.bin

And submit it by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx3.bin http://localhost:20443/v2/transactions

Finally, we can issue a third transaction, reading the key foo again, for ensuring that the previous transaction has successfully updated the state machine:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 3 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store get-value -e \"foo\" --testnet | xxd -r -p > tx4.bin

And submit this last transaction by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx4.bin http://localhost:20443/v2/transactions

Congratulations, you can now write your own smart contracts with Clarity.

Platform support

Officially supported platforms: Linux 64-bit, MacOS 64-bit, Windows 64-bit.

Platforms with second-tier status (builds are provided but not tested): Linux ARMv7, Linux ARM64.


Beyond this Github project, Blockstack maintains a public forum and an opened Discord channel. In addition, the project maintains a mailing list which sends out community announcements.

The greater Blockstack community regularly hosts in-person meetups. The project's YouTube channel includes videos from some of these meetups, as well as video tutorials to help new users get started and help developers wrap their heads around the system's design.

For help cross-compiling on memory-constrained devices, please see the community supported documentation here: Cross Compiling.

Further Reading

You can learn more by visiting the Blockstack Website and checking out the documentation:

You can also read the technical papers:

If you have high-level questions about Blockstack, try searching our forum and start a new question if your question is not answered there.


Tests and Coverage

PRs must include test coverage. However, if your PR includes large tests or tests which cannot run in parallel (which is the default operation of the cargo test command), these tests should be decorated with #[ignore]. If you add #[ignore] tests, you should add your branch to the filters for the all_tests job in our circle.yml (or if you are working on net code or marf code, your branch should be named such that it matches the existing filters there).

A test should be marked #[ignore] if:

  1. It does not always pass cargo test in a vanilla environment (i.e., it does not need to run with --test-threads 1).
  2. Or, it runs for over a minute via a normal cargo test execution (the cargo test command will warn if this is not the case).


This repository uses the default rustfmt formatting style. PRs will be checked against rustfmt and will fail if not properly formatted.

You can check the formatting locally via:

cargo fmt --all -- --check

You can automatically reformat your commit via:

cargo fmt --all

Copyright and License

The code and documentation copyright are attributed to for the year of 2020.

This code is released under the GPL v3 license, and the docs are released under the Creative Commons license.