Overview
Gerolamo lets app builders run a blockchain node on their own computer and pull blocks, balances, and transactions from it instead of relying on someone else's server. A node is the program that keeps a copy of a network's shared record and trades updates with other copies. Written in TypeScript so web developers can read how it works, Gerolamo is still in development at Harmonic Labs1, a development studio that builds TypeScript tools for Cardano.
Gerolamo is one of several Cardano node implementations built as alternatives to the reference node software. Harmonic Labs argues that several independently built nodes, which developers call client diversity, reduce single points of failure on the network2. The longer-term aim is a light node, a node small enough to run inside a web browser, giving wallets and decentralized apps (DApps) direct access to Cardano without a central server3.
Key Features
- Your own source of chain data. Gerolamo connects to other Cardano nodes, downloads new blocks, and stores them in SQLite, a lightweight database that lives in a single file on your machine1.
- Familiar data lookups for apps. A built-in API, a set of web addresses other programs can call, returns blocks, balances, and transactions and sends signed transactions out1. It also covers part of the Blockfrost interface, a common way apps request chain data1.
- Faster first setup. Instead of downloading the whole chain from peers, Gerolamo can start from a Mithril snapshot, a certified copy of the chain, or rebuild its data from chain files already on disk1.
- A visual control panel. A desktop Control Center app and a local stats page show the newest block, connected peers, and other health numbers without any command-line work1.
- Hooks for existing Cardano tools. An optional local socket, the private connection that wallets and other tools expect a node to offer, lets nearby programs follow the chain and submit transactions1.
What to Expect
Gerolamo's code, documentation, and setup instructions live in its public GitHub repository1. Developers install Bun, a runtime that executes JavaScript and TypeScript, then start a node on Cardano's preprod test network or on mainnet with a single command1. The node then serves its data at a local web address on the same machine.
Teams building apps can embed Gerolamo instead of running it by hand. A dedicated guide explains how a host app starts an instance, checks its health, reads its data, and shuts it down, the same pattern Harmonic Labs follows in The Lab, its own app that starts and manages Gerolamo nodes4. The same guide spells out that Gerolamo is a relay and data node, which follows the network and serves chain data to apps, not a drop-in replacement for the standard Cardano node4. Developers who need more than a node can pair it with Buildooor, the Harmonic Labs library for assembling Cardano transactions in TypeScript.
Gerolamo Pool (ticker GERO) is a test stake pool on Cardano's Preview test network. Its Cexplorer page links to the Gerolamo repository and lists the blocks the pool has produced5.
The work behind Gerolamo was funded by Project Catalyst grants, voted on by the Cardano community, including one for its networking layer6. Harmonic Labs also secured Cardano treasury funding through the 2025 budget process run by Intersect, a member-driven Cardano organization7.
