Building a Web3 CLI Tool for the Ballerina Language: From Idea to Reality

🚀 Excited to finally share my journey of building a web3 CLI tool for Ballerina! This tool bridges the gap between Ethereum smart contracts and the Ballerina programming language by automatically generating a Ballerina connector from any given smart contract.

In this post, I’ll walk you through:

Why I built this tool

The technologies involved

The challenges I faced (and how I solved them)

How it all works under the hood

🌐 Why a Web3 Tool for Ballerina? Ballerina is a modern programming language designed for integration. With its powerful built-in concurrency and network primitives, I saw a huge potential for it to be used in blockchain-related applications.

However, Ballerina lacked official tools to interact with Ethereum smart contracts — unlike other ecosystems like JavaScript or Python.

So I decided to build a solution: a CLI tool that can automatically generate Ballerina code for any smart contract using its ABI file — just like the Ballerina OpenAPI tool does for REST APIs.

🔧 Technologies Used Here’s what I used to bring this project to life:

Technology Purpose Java CLI tool development, ABI parsing, codegen Ballerina Target language for generated code Ballerina Syntax Tree API To generate Ballerina syntax programmatically Solidity Smart contract language Ganache Local Ethereum blockchain for testing PicoCLI CLI parsing framework in Java 🛠 How It Works Parse the Smart Contract ABI The user provides an ABI file (JSON) exported from Solidity. The tool parses this ABI to extract all the functions, inputs, and outputs.

Generate Remote Functions For each method in the smart contract, the tool creates a corresponding remote function in Ballerina with proper types and structure.

Sanitize Solidity Identifiers Some Solidity identifiers (like match, type, etc.) are reserved keywords in Ballerina. I added a sanitizer step to rename or safely transform them during generation.

Use Ballerina Syntax Tree API This part was the most complex. I had to dynamically build Ballerina code from Java using the official Syntax Tree API. This allows the tool to generate clean, valid, and idiomatic Ballerina code.

Output the Connector The final result is a fully functional Ballerina connector module that can:

Call contract functions (view or state-changing)

Fetch Ethereum accounts

Query blocks and transactions

Interact with events (coming soon)

🧪 Crypto Hurdle: No Keccak-256? One major roadblock I hit early on was that Ballerina didn’t support Keccak-256 hashing, which is essential for generating Ethereum function selectors.

✅ So I decided to contribute to the Ballerina Crypto Library myself and added Keccak-256 support! This contribution made the rest of the work possible.

💡 Challenges Faced

Challenge How I Solved It ABI parsing and type mapping Wrote a custom parser to map Solidity types to Ballerina types Reserved keywords in Ballerina Built a sanitizer for identifiers Code generation via Java Learned and used the Ballerina Syntax Tree API Function selector hashing Added Keccak-256 to the Ballerina crypto module CLI integration Used PicoCLI for a clean and user-friendly CLI interface 🧰 Sample Usage

java -jar ballerina-web3-cli.jar \
  --abi /path/to/MyContract.abi.json \
  --output ./generated \
  --package mycontract

This command generates a full Ballerina module named mycontract with all the functions from the smart contract!

🔗 GitHub Repository You can check out the tool on GitHub: 👉 https://github.com/SkFatharAli/web3-ballerina

Feel free to explore, give feedback, or even contribute.

🙌 Final Thoughts This project pushed me to learn new things—from ABI parsing to language internals to writing Ballerina from Java. But it was worth every bit of effort.

Ballerina has great potential in the blockchain ecosystem. With this tool, I hope to make smart contract integration easier and faster for everyone using Ballerina.

If you’re building something similar or curious about Ballerina + Web3 — I’d love to connect!

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