Show HN: Endo – A Higher-Order Harness

Developer longsurf-ai released Endo, an open-source "Higher-Order Harness" (HOH) agent orchestration layer built on Effect, which treats an entire agent the same as a single LLM call to allow arbitrary composition of agent workflows. Endo provides a single UI for using any agent provider with existing subscriptions and hot-swapping agents mid-session, plus an agent protocol that abstracts any harness so raw models and agents behave identically in a KV-cache-friendly manner. The project grew out of the developer's work on OpenChart, where trading workflows required strict determinism alongside inference-time decision-making.

Endo is a Higher-Order Harness HOH . From the easiest concept to understand to the more complex ones, Endo gives you: A single, simple UI to use any agent provider with your existing subscriptions, and hot-swap agents right in the middle of a session. An orchestration layer, which I call HOH, allowing arbitrary composition of agents to achieve any workflow. A fun case I tried was asking Fable and Astra to mock a presidential debate. An agent protocol that abstracts any agent. The key insight here is that every LLM is an agent—instead of treating the LLM as just one node inside an external ReAct loop. Endo was a concept formed while I was building OpenChart https://github.com/longsurf-ai/openchart https://github.com/longsurf-ai/openchart . To power trading workflows, I needed to support scenarios where strict determinism is required, while still keeping the flexibility of an agent's inference-time decision-making capability. A new form factor was needed between rigid n8n-style workflows and open-ended ReAct loop agents. Thus the creation of Endo. Endo is short for Endomorphism, a term rooted in category theory and functional programming. An endomorphism is a function that transforms an object into another object of the same type. Similarly, Endo itself is built purely on functional programming principles, relying heavily on Effect https://github.com/Effect-TS/effect https://github.com/Effect-TS/effect . ..And if you have patience to speak technical jargons, Endo is: An agent orchestration layer—Higher-Order Harness HOH —where an entire agent is treated the same as a single LLM call, enabling arbitrary composition of extremely complex workflows. A way to abstract any harness into a standardized protocol, where raw models and agents behave the exact same way, in a KV-cache-friendly manner. A workflow engine that enables arbitrary composition of agents with a single workflow language. It's completely open source, and if you think this idea is cool, let's build together. Just for the fun of it. Comments URL: https://news.ycombinator.com/item?id=50110614 https://news.ycombinator.com/item?id=50110614 Points: 2 Comments: 0