What we learned building 100 API integrations with OpenCode

Summary

At Nango, we build open source infrastructure for product integrations.With all the recent advancements in coding models, we wanted to see how far we can push an autonomous agent building integrations with external APIs.TL;DR: Our background agent isn’t perfect, but it reliably generates ~200 integrations across five APIs (Google Calendar, Drive, Sheets, HubSpot, and Slack) in 15 minutes and less than $20 in token costs.Previously, this would have taken an engineer about a week.This post is about what it took to get there, what broke along the way, and what we learned building a background coding agent for API integrations.Try it yourself: Our Nango AI builder lets you build custom API integrations with the skills from this article.Our setupThe pipeline is pretty simple:We define a list of interactions to build, for example create-calendar-event, sync-files, or send-slack-messageOur orchestrator prepares one workspace per interaction with the right Nango integrations scaffolding generated by our CLIWe spawn one OpenCode agent per interactionEach agent independently builds its interaction, tests it with the external API (the agent has access to a test account), and iterates until it worksOnce all agents finish, the orchestrator checks their work and assembles the individual interactions into one Nango integration per APITo make our learnings reusable for customers, we rely heavily on skills. They are easy to publish, work across agents, and adapt to different use cases through a prompt that references them.The spec for each interaction is really simple: { "id": "create-event", "displayName": "Create Event", "description": "Create a calendar event", "prompt": "As a pre-requisite create a calendar first", "comments": "" }, Besides the description of the interaction, we also pass the agent information about the API docs and how to load a test connection (=test account) from Nango: connection_id: bff8b7b7-cb26-443f-9a3a-ec11a5d4d6ff integration_id: google-calendar env: d...