Building and Testing Canton Smart Contracts Locally

Written by: Tushar Sharma

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Building on Canton requires fast feedback loops. Testing locally before deploying to a testnet saves time and costs. This guide walks through a complete workflow: create a contract, build it, spin up a sandbox, and verify it works via the JSON API.

Step 1: Initialize Your Project

            mkdir -p testContract
cd testContract
daml init

          

This creates the boilerplate:

            testContract/
├── daml.yaml         # Project metadata
└── daml/
    └── Main.daml     # Smart contract code

          

Step 2: Write a Simple Asset Contract

Create daml/Main.daml:

What this does:

Template Asset: Represents an asset with owner, name, and value
signatory owner: Only the owner can authorize contract creation
choice Transfer: Lets the owner transfer the asset to someone else

Step 3: Build the Contract

daml build

Output:

            2026-04-07 20:17:41.33 [INFO] [build]
Created .daml/dist/testContract-1.0.0.dar

The .dar file (DAML ARchive) is like a JAR—it bundles your compiled smart contract.

Step 4: Automate with a Makefile

Create a Makefile at the project root:

Step 5: Run the Sandbox

make start

This builds your contract and spins up:

Ledger API on localhost:6865
JSON API on localhost:7575

Step 6: Verify It Works

Test the JSON API health check:

curl http://localhost:7575/readyz

Response:

            [+] ledger ok (SERVING)
readyz check passed

Check the version:

curl http://localhost:7575/v2/version

You'll get detailed ledger capabilities. If both curl commands succeed, your sandbox is live.