Harness Engineering - Part 4: The Tool Layer

<p><em>Welcome back to the Harness Engineering series — a 10-part journey from raw language model to production-ready agentic system. Made by builders. For builders.</em></p>

<p>Claude's tool use (function calling) API is what separates toy chatbots from actual agents. I've built production agents with it — here's what reliable tool use looks like when

<table> <tr><td> <a href="https://www.reddit.com/r/LocalLLaMA/comments/1wxfdt9/qwen38_27b_1_x_r9700_262k_context_half_a_million/"> <img alt="Qwen3.8 27B | 1 x R9700: 262K context,

<h3> For a more in-depth guide </h3> <p>Medium: <a

<p>Now that we understand what MCP is, let’s focus on the most important concept:</p> <blockquote> <p><strong>Tools</strong></p> </blockquote> <p>If MCP is the system,<br /> tools

<p><em>Welcome back to the Harness Engineering series — a 10-part journey from raw language model to production-ready agentic system. Made by builders. For builders.</em></p>

<p><em>Welcome back to the Harness Engineering series — a 10-part journey from raw language model to production-ready agentic system. Made by builders. For builders.</em></p>

<p>Now I have the freshest 2025–2026 data. Let me write the fully verified, trend-accurate, non-repetitive final version:</p> <h1> Tool Calling in AI Agents: LangChain, LangGraph,