AgentsSeptember 14, 2026via MarkTechPost
Agent Harness vs Agent Framework vs MCP: Which Layer Owns the Loop, State, Tools, Permissions, and Recovery
Why it matters
As agents move from prototype to production, practitioners need to understand which layer—harness, framework, or MCP—owns critical responsibilities like state management, tool binding, permissions, and recovery. This is the architectural literacy that separates pilot projects from deployable systems.
Key signals
- Three-layer agent architecture: harness (loop/orchestration), framework (model integration), MCP (tool/resource protocol)
- Harness owns: the execution loop, state persistence, error recovery, and multi-turn orchestration
- Framework owns: model routing, prompt composition, and output parsing
- MCP owns: tool discovery, permissions enforcement, and resource binding
- Overlap analysis between layers identifies deployment risk points
- Published Sep 14, 2026 — timely for production agent rollouts
- Three-layer agent stack taxonomy: harness (orchestration/loop control), framework (agent logic/tools), MCP (protocol/integration)
- State management ownership unclear across layers — critical for production reliability
- Tool access and permissions split between framework and harness in most deployments
- Recovery and error handling responsibility varies by implementation — a risk for autonomous workflows
- MCP (Model Context Protocol) as a standardization play for agent-tool boundaries
The hook
The agent stack has three layers. Most teams are building in the wrong one.
A practitioner's map of the 3 layers in a modern agent stack, with verified sources and an overlap analysis.