Claude-powered agents that use MCP servers to connect to your databases, APIs, and external services, the architecture that makes Claude genuinely useful for multi-step operational tasks rather than just text generation. Claude's tool use (function calling) allows the model to invoke defined tools mid-completion, process the results, and continue reasoning: a procurement agent that queries your ERP for inventory levels, checks supplier lead times via API, and creates a purchase order recommendation is a practical workflow that Claude can execute reliably when the tools are well-designed and the system prompt defines the agent's decision authority clearly. MCP (Model Context Protocol) as the tool connectivity standard: each external system (your PostgreSQL database, your CRM API, your document store) exposed as an MCP server with defined resources and tools; Claude connects to MCP servers at inference time and queries them within the conversation turn. Agentic architecture patterns built on LangGraph: stateful multi-step agents where each step involves a Claude API call, tool execution, and a routing decision based on the result, with explicit human-in-the-loop gates at high-stakes decision points (e.g., "this action will delete records, confirm before proceeding"). Tool design principles that make Claude agents reliable: narrow tool scope (each tool does one thing), structured input and output schemas (JSON Schema enforced), idempotency for state-modifying tools (the same tool call with the same parameters produces the same result on retry), and explicit error messages that give Claude enough context to recover gracefully rather than repeating a failed tool call. Production deployment with tool call logging: every tool invocation logged with the input parameters, output, latency, and the Claude turn that triggered it, the audit trail for operational agents where tool calls have real-world consequences.