Hyperledger Cacti | Mentorship Program

Connecting Chains: Building a Polkadot Connector for Hyperledger Cacti

Anmol Bansal, Hyperledger Cacti Contributor and Full Stack Web3 Developer at Holonym Foundation |
Connecting Chains: Building a Polkadot Connector for Hyperledger Cacti

As blockchain ecosystems evolve, interoperability between networks is becoming increasingly vital. During the 2023 Hyperledger Mentorship Program, I had the opportunity to contribute to this vision by developing a Polkadot connector for Hyperledger Cacti, a platform now hosted by LF Decentralized Trust that facilitates interactions across heterogeneous distributed ledgers.

This post shares the journey of designing and implementing the connector — its goals, core features, and the impact of open collaboration within the LF Decentralized Trust community.

Why Polkadot? Why Now?

While Hyperledger Cacti already supported major chains like Ethereum and Hyperledger Fabric, integration with the Polkadot ecosystem, which is built using the Substrate framework,remained unexplored. Given Polkadot’s modular, scalable, and parachain-centric architecture, enabling Cacti to interface with Substrate-based chains opens the door to a wide range of cross-chain applications.

The primary aim was to build a connector that supports essential blockchain operations such as querying account balances and submitting transactions and to lay the foundation for more advanced interoperability features.

What We Built: Features and Technologies

The connector, implemented in TypeScript, integrates with the Cacti plugin framework and uses the Polkadot JS API SDK to communicate with Substrate nodes.

Key technical highlights include:

  • Balance and Block Queries: Using the RPC calls and block retrieval via finalized block hashes.
  • Transaction Submission: Signing and sending transactions through a local signer wrapper.
  • Chain Metadata Parsing: Exposing runtime methods and constants through metadata inspection.
  • OpenAPI Spec Support: Auto-generating standardized documentation for connector routes.
  • Prometheus Metrics: Integrating connector health and usage stats to improve observability.
  • Health Check Endpoint: Including built-in HTTP endpoint for service uptime monitoring.
  • Test Environment Setup: Adding Docker-based Substrate node for local development and testing.
  • Test Coverage: Ensuring core operations are covered with Jest-based unit test cases.

The connector exposes an Express-compatible web service layer, enabling external applications to interact with Substrate chains via HTTP calls. Each route follows the Cacti plugin conventions for consistency and ease of use.

Working with the Community

Continuous feedback from the Cacti maintainers drove the evolution of the connector’s design and integration. Their input during bi-weekly check-ins, code reviews, and community discussions helped refine the implementation and align it with Cacti's modular architecture.

The project also included creating documentation and usage examples, including this detailed developer guide. These resources aim to make the connector accessible to both new contributors and users.

The experience underscored the importance of building in the open—from design reviews to collaborative debugging sessions.

This work was made possible by the guidance of mentors Jagpreet Singh and Peter Somogyvari, whose technical direction and feedback were instrumental throughout the project. I would also like to thank Rafael Belchior and Catarina Pedreira for their foundational work that laid the groundwork for the connector’s architecture.

Broader Impact

By bridging Polkadot with the interoperability layer of Hyperledger Cacti, this connector sets the stage for:

  • Enterprises to explore cross-chain data sharing and tokenization use cases
  • Developers to extend Cacti with parachain-specific logic

While the project began under the scope of a mentorship, it has continued to grow through sustained community involvement. Contributions now include metrics, testing utilities, and plans for RPC extensions.

You can view the merged pull request here: hyperledger-cacti/cacti#2877.

Closing Thoughts

Building the Polkadot connector for Hyperledger Cacti has been a rewarding experience in both technical and collaborative dimensions. It offered exposure to Substrate internals, SDK usage, containerized blockchain development, and open-source workflows.

The connector is now available as a plugin within the Cacti ecosystem, and I hope it continues to serve as a base for future development and innovation in cross-chain systems.

The code, setup instructions, and contributions can be found in the Hyperledger Cacti repository.
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