Quick Start - Writz Protocol

Building on Writz from your own project? This page is the contributor guide: it builds and tests this repository. To call the deployed contracts from your app or your Soroban contract, start with Build on Writz. AI coding agents: For AI Agents.

The core lending and verification logic in this repository is working code, not a mockup: the contracts are deployed on Stellar testnet, and the tests pass (see docs/developers/runbook.md). Writz v1 is bitcoin-spv and writz-lend; zk-verifier, commitment-tree and the circuits, all under privacy/, belong to the separate privacy edition, in progress and testnet only. writz-lend/src/oracle.rs’s get_btc_price_stroops now calls a real Reflector oracle on testnet (see docs/research/oracle-design.md) - the privacy edition’s commitment-tree still returns a hardcoded price; it is not part of v1. Start here and have something running in under 5 minutes.

Prerequisites

Install the following before proceeding:

# Rust + WebAssembly target
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
rustup target add wasm32v1-none

# Stellar CLI (version 27 or later)
# macOS
brew install stellar-cli
# Linux
cargo install --locked stellar-cli

# Node.js 20+
# https://nodejs.org/

# Bun 1.1+ - bitcoin-script, relayer, frontend and packages/* install with Bun,
# not npm. Only privacy/circuits/ is npm-managed.
curl -fsSL https://bun.sh/install | bash

# circom (for ZK circuit tests only).
# circom 2.x is a Rust binary. `npm install -g circom` installs the legacy 1.x
# package and CANNOT compile `pragma circom 2.0.0` - use the release binary:
curl -fL -o ~/.local/bin/circom \
  https://github.com/iden3/circom/releases/download/v2.2.3/circom-linux-amd64
chmod +x ~/.local/bin/circom   # macOS: use circom-macos-amd64
circom --version               # expect: circom compiler 2.2.3

# snarkjs needs no global install - it is a dependency of privacy/circuits/

Clone the Repository

git clone https://github.com/WritzProtocol/writz.git
cd writz

Run All Tests

Soroban contracts (Rust)

cd contracts
cargo test

Expected output: 263 tests pass across bitcoin-spv (68), zk-verifier (26), commitment-tree (59), writz-lend (100), and spv-types (10).

Bitcoin script toolkit (TypeScript, Bun)

cd bitcoin-script
bun install
bun test

Expected output: 60 tests pass.

Relayer service (TypeScript, Bun install + Jest)

The relayer installs with Bun but its suite is Jest (ts-jest), so it must run through the package script - plain bun test selects Bun’s own runner and fails. It also imports the local @writz/* packages via their built dist/ output, so build those first.

cd privacy/packages/commitment-tree && bun install
cd ../../../bitcoin-script && bun run build
cd ../relayer && bun install && bun run test

Expected output: 248 tests pass.

ZK circuits (Circom + snarkjs, npm)

cd privacy/circuits
npm install
npm test

Expected output: 52 tests pass (proof generation, commitment correctness, ratio enforcement, nullifiers). If verify() assertions fail here while prove() succeeds, your local privacy/circuits/keys/*_final.zkey (gitignored, regenerated locally) is out of sync with the committed privacy/circuits/keys/*_vkey.json. Run bash scripts/compile_all.sh && bash scripts/setup_dev.sh to regenerate both together from a fresh dev trusted setup, then re-run npm test.

All together: 623 tests, all passing.

Build the Contracts

cd contracts
stellar contract build
cd ../privacy/contracts
stellar contract build

This produces Wasm artifacts in contracts/target/wasm32v1-none/release/:

bitcoin_spv.wasm - 28.4 KB
writz_lend.wasm - 23.7 KB

and, for the privacy edition, in privacy/contracts/target/wasm32v1-none/release/:

zk_verifier.wasm - 11.8 KB
commitment_tree.wasm - ~38 KB

Use the Testnet Deployments

All four contracts are live on Stellar testnet. You can call them directly without deploying:

# Check the SPV contract is alive
stellar contract invoke \
  --id CBX23YKCCJMAMBMSCNP6YVKEXUIYK2CTKSR4TQ3RVBPAFYZFVCW7W4EO \
  --network testnet \
  -- get_version

# Check the Merkle root
stellar contract invoke \
  --id CAQBLCAPGXXCZTJDAJLY7E4PTJYGR6CY4YWH4JSJKFXYIHW3GANP6RFM \
  --network testnet \
  -- get_merkle_root
# Returns: 0x2134e76ac74b4b8765b6e37992aa15f0... (Poseidon-2 empty tree root)

Run the Privacy Edition End-to-End Flow

scripts/deploy/e2e_local.mjs deploys all four contracts through their constructors on a local Stellar network, registers the verification keys and runs deposit → borrow → repay → release with real Groth16 proofs. It also replays the closed attacks (a deposit claiming someone else’s output, a redirected borrow, a re-borrow after release, the same txid in both lenders) and expects each to fail. CI runs it as the e2e-local job. No testnet account or real keys are involved.

docker run -d --rm --name writz-local-stellar -p 8000:8000 \
  stellar/quickstart:latest --local --enable rpc
(cd contracts && cargo build --release --target wasm32v1-none --locked)
(cd privacy/contracts && cargo build --release --target wasm32v1-none --locked)
(cd privacy/circuits && npm ci && npm run compile && npm run setup:dev)
(cd scripts/deploy && bun install)
node scripts/deploy/e2e_local.mjs

npm run setup:dev regenerates the development keys in privacy/circuits/keys/; restore the committed ones afterwards with git checkout privacy/circuits/keys.

Run the Bitcoin P2WSH End-to-End

This script tests the Bitcoin locking and release flow on Bitcoin Signet. No funds required for a dry run.

cd bitcoin-script
npm run build

# Dry run - builds and inspects the P2WSH transaction without broadcasting
node scripts/e2e_testnet.mjs --dry-run

# Live broadcast (requires Signet BTC - get from a Signet faucet)
node scripts/e2e_testnet.mjs

The live broadcast will:

Generate a unique P2WSH address
Send Signet BTC to the address
Build the Path A co-signed release transaction
Sign with both user and protocol keys (PSBT round-trip)
Broadcast to Bitcoin Signet

Reference transactions (already executed on Bitcoin Signet):

Funding: 61deea44
Release: 11932100

Deploy Your Own Contracts

scripts/deploy/deploy_stack.mjs deploys and wires up all four contracts in the order they depend on each other. Without --execute it only validates its inputs and prints the plan. Set STELLAR_NETWORK=local to rehearse against the local network above. The inputs are listed in scripts/deploy/.env.example.

(cd contracts && cargo build --release --target wasm32v1-none --locked)
(cd privacy/contracts && cargo build --release --target wasm32v1-none --locked)
cd scripts/deploy
node deploy_stack.mjs             # validate and print the plan
node deploy_stack.mjs --v1-only   # bitcoin-spv and writz-lend only
node deploy_stack.mjs --execute   # deploy

Do not deploy to the shared testnet or to mainnet without the project owner’s sign-off.

Repository Layout for Developers

contracts/
  contracts/
    bitcoin-spv/src/
      lib.rs        - public contract interface
      header.rs     - Bitcoin block header parsing + PoW verification
      merkle.rs     - Merkle proof verification
      crypto.rs     - SHA256d implementation in Soroban Wasm
      types.rs      - Config, Checkpoint (SpvVerificationResult now lives in the shared `spv-types` crate)
    writz-lend/src/
      lib.rs        - non-ZK lending skeleton
      rates.rs      - kinked interest rate model

privacy/contracts/
  zk-verifier/src/
    lib.rs        - verify_deposit(), verify_borrow_repay(), set_verification_key()
  commitment-tree/src/
    lib.rs        - deposit(), borrow(), repay(), liquidate()
    oracle.rs     - SEP-40 oracle interface

privacy/circuits/
  src/
    deposit.circom      - Deposit ZK circuit
    borrow_repay.circom - Borrow/Repay ZK circuit
    liquidation.circom  - Liquidation ZK circuit
    merkle.circom       - Shared Poseidon Merkle components
  keys/
    deposit.vkey.json       - Deposit verification key
    borrow_repay.vkey.json  - Borrow/Repay verification key
    liquidation.vkey.json   - Liquidation verification key

relayer/src/
  index.ts      - Express API: GET /spv-proof/:txid
  spv.ts        - SPV proof assembly (Esplora + Merkle computation)
  bitcoin.ts    - Bitcoin types and parsing

bitcoin-script/src/
  script.ts     - P2WSH redeem script builder
  address.ts    - Deposit address derivation
  spend.ts      - Path A/B PSBT signing
  keys.ts       - Key management utilities

Next: Bitcoin SPV SDK →

​Prerequisites

​Clone the Repository

​Run All Tests

​Soroban contracts (Rust)

​Bitcoin script toolkit (TypeScript, Bun)

​Relayer service (TypeScript, Bun install + Jest)

​ZK circuits (Circom + snarkjs, npm)

​All together: 623 tests, all passing.

​Build the Contracts

​Use the Testnet Deployments

​Run the Privacy Edition End-to-End Flow

​Run the Bitcoin P2WSH End-to-End

​Deploy Your Own Contracts

​Repository Layout for Developers