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What is Yielded Agent?
Yielded Agent (formerly Effect Agent) is an agent harness toolkit for TypeScript, built on Effect and Effect AI. You supply a model, tools, instructions, and input/output schemas. It runs the agent loop, executes tool calls, and validates the result.
What it adds to Effect AI
Section titled “What it adds to Effect AI”Effect AI provides models, tools, and provider integrations. Yielded Agent uses those directly and adds:
- Durable execution to recover accepted work after a crash on Node.js or Cloudflare.
- Limits on turns, tool calls, time, and token usage.
- Streaming events and approvals to observe and control a run.
- Context management to prune and summarize long threads.
- Subagents for delegation with explicit permissions and budgets.
- Thread history across runs.
- Code Mode for generated JavaScript that reads and changes application data through authorized tools.
- Sandbox execution and browser tools for process output, rendered pages, crawling, and scoped browser interaction.
It runs in Effect
Section titled “It runs in Effect”AgentRuntime.run returns an Effect; AgentRuntime.stream returns a Stream.
Tool errors stay typed, required services stay visible, and interruption runs resource finalizers.
Supply dependencies through Layers, including test models that need no API keys.
Your application supplies credentials, tool handlers, and authorization. The package map covers adapters and limitations.