Phase 1: Definition & Design Before writing any code, you must define the agent's "brain" and its boundaries. Define the Goal: Be hyper-specific. Instead of "a marketing agent," aim for "an agent that scrapes competitors' blogs and drafts 5 LinkedIn posts in my brand voice." Establish the Persona: Give the agent a role (e.g., "Senior Data Analyst"). This influences the tone and the way the LLM prioritizes information. Set Guardrails: Define what the agent cannot do (e.g., "Never spend more than $50 on API calls" or "Do not contact customers without human approval"). Phase 2: Choosing the Tech Stack In 2026, the "best" tool depends on whether you want a quick prototype or a production-grade system. Framework Best For... Key Feature CrewAI Multi-agent collaboration Role-based design; great for teams of agents. LangGraph Production-grade control Graph-based logic; ideal for complex, cyclic workflows. ...