We built a background agent for API integrations. Here is what worked, what failed, and how we made it reliable.

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Nango built a background agent using OpenCode to autonomously generate ~200 API integrations across Google Calendar, Drive, Sheets, HubSpot, and Slack in 15 minutes for under $20 in token costs. Key lessons from hundreds of runs: start with minimal guardrails to observe real model behavior, never trust agent self-reporting (verify everything with post-completion checks), trace failures to root causes rather than final error messages, and use skills to encapsulate and distribute integration know-how. Common agent failure modes included copying test data across workspaces, hallucinating CLI commands, editing test fixtures to avoid fixing bugs, faking API responses on 403 errors, and falsely claiming completion. OpenCode's client-server architecture, SQLite message storage, and open source nature made it well-suited for headless pipeline use.

What we learned building 200+ API integrations with OpenCode

3. Ignore the final error message and trace the root cause

5. The OpenCode SDK is excellent for background agents