Justin
Farr-Jones
I finance, build and fix companies.
Deal-led co-founder and operator. Twenty years across private equity, emerging markets, fintech and AI, from €2 billion of leveraged buyouts to the board of the company behind one of TypeScript's most-used libraries. Based in London.
Twenty years, by capital
Each line is a role. The figure is the capital I was responsible for or raised. Select a line for the detail.
Effectful Technologies 2023–now
Board member of a developer-tools company backed by Amplify Partners. Advised on fundraising. Its open-source TypeScript library has about 43.9 million weekly downloads (Effectful, September 2026).
Now
- Non-Executive Director, Effectful Technologies
- The Effect TypeScript library was incubated and funded at my fintech, Creditscript, led by our then CTO Michael Arnaldi, building on fp-ts. Effectful, backed by Amplify Partners, now carries it forward; the library has about 43.9 million weekly downloads (Effectful, September 2026).
- Building agentic AI
- Advising clients on agent systems and prototyping them myself in TypeScript, Python and Rust: memory stores, security and agent-to-agent frameworks.
- Looking for the next company
- A co-founder seat at a well-funded AI, fintech or proptech company, an operating role at a PE-backed business, or a transaction mandate. See how I can help.
Writing
- Poppy, read closely: a builder's notes on the Personal Agent ProtocolI build agent systems, so I read the Poppy specification line by line. Most of its design choices are good ones. Three need fixing before anyone should trust it with money.
- Your customer's agent is at the door: what the Personal Agent Protocol means for consumer financial servicesMeta and Sierra have published a draft standard for how personal AI agents sign in to businesses. Banks, lenders and insurers should read it closely. It answers the easy questions and leaves the regulated ones open.
- Hire contractors, not employees: why A2A and ephemeral workers are the future of AI agentsAn opinion. The winning agent architecture will not be one all-knowing assistant with standing access. It will be short-lived, single-purpose workers that talk to each other through open protocols.