0006 Scrolls Custom Indexing

Custom Blockchain Indexing on Cardano


This RFC proposes a mechansim to simplify the creation of custom indexes for Blockchain data in the Cardano ecosystem. The proposed system offers a unique approach that balances lightweight flexibility and specific use-case requirements.


Currently, indexing chain data presents significant challenges, primarily because every project has unique requirements. Existing indexing solutions are either too cumbersome or lack necessary features. The solution? We propose a framework that allows projects to define data filtering and aggregation logic in a concise Typescript file, utilizing the Map / Reduce algorithm. This tool then performs custom indexing and exposes a GraphQL API, thereby providing a bespoke solution for each project's needs.

Problem Context

Chain data is vast and constantly growing. The full ledger structure is intricate, and most dApps only need a small fraction of the on-chain data relevant for their use-case. The current tools available attempt to offer one-size-fits-all solutions, which either require extensive storage and compute resources or provide limited query options.

The Ideal Scenario

The ideal scenario is to have a tailored database for each dApp, containing only the relevant chain subset and designed specifically for the dApp's needs. Boilerplate code and infrastructure plumbing should be readily available through an SDK. Developers can then focus on adapting the SDK to their dApp's specific requirements. The solution should also include an easy and flexible querying system, ideally via a GraphQL endpoint. The deployment of such a solution should be straightforward and well-documented, with the added option of infrastructure service providers offering "indexing" clusters that can plug-and-play custom code for client dApps.

Use Cases

The proposed solution can benefit a variety of applications, including:

  • A DEX could create custom indexes for their liquidity pools and swap transaction history.
  • An NFT marketplace could create custom indexes for available collections, bidding prices, total supply, and transaction history.
  • An Oracle could create custom indexes for the current value and history of past values for their fact statement catalogs.
  • ADA Handles could be represented by a custom index that maps handles to the latest address.
  • A dApp that requires batching of UTxOs could create custom indexes to keep track of relevant UTxO required for their batching purposes.

Technical Plan

We aim to build an open-source indexing engine, based on a modified version of Scrolls, that supports plugins. These plugins will run using either the Deno runtime or a WASM runtime, with each plugin providing two functions: "Map" and "Reduce". The indexing engine will crawl through the history of the chain, executing the Map / Reduce operations for each block. The output will then be stored in a relational database. Furthermore, we will integrate existing GraphQL libraries that automatically generate APIs from existing database schemas.

Benefits to the Cardano Ecosystem

By solving one of the primary challenges of building dApps in Cardano, we are empowering developers to write less boilerplate code, focus more on core-business propositions, and simplify the onboarding process when starting to work on the Cardano ecosystem. By providing a validated solution similar to those already applied in other blockchain ecosystems, we aim to reduce the developer-experience gap that Cardano has compared to other ecosystems and simplify the migration of projects already building in other ecosystems that wish to integrate Cardano.

Measuring Success

We plan to measure the success of the project by monitoring activity in the open-source GitHub repository, the number of external repositories that include this project as a dependency, and the number of dApp projects using this feature through the hosted version at Demeter.run.

Delivering the Project with High Levels of Trust and Accountability

TxPipe, the team behind this project, has a strong track record of contributing to the Cardano ecosystem. Examples of our contributions include Pallas, a Rust library for Cardano used by several high-profile projects, and Oura, an off-chain data integration tool for Cardano used by many projects in the community. Our past achievements demonstrate our commitment to the Cardano community and the technical expertise required to develop and maintain Cardano infrastructure.


In conclusion, our proposal to create custom indexes for Blockchain data aims to bring significant value to the Cardano ecosystem. By simplifying the process of creating chain indexers that are lightweight, flexible, and performant, we believe we can help the ecosystem grow and thrive.