PART 2 — Taxonomy: What Kind of Agent Are You Building?

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The 5 Levels — From Brain to Self-Evolving System

The Intuition

Think of hiring: you wouldn't hire a contractor without knowing the job scope. Same here — pick the right level of agent for the complexity of the task.

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Level 0: Core Reasoning System (The Encyclopedia)

• What: LLM alone, no tools, no memory
• What it can do: Answer from training data
• Production use: FAQ chatbot on known, static content
• Limit: Knowledge cutoff. Can't act. Can't look things up.

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Level 1: The Connected Problem-Solver

• What: LLM + external tools (Search, Calculator, DB queries)
• What it can do: Answer about real-time events, current data
• Production use: Customer support agent that can look up order status
• Technique: Function calling — the LLM decides which tool to use, ADK executes it

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Level 2: The Strategic Problem-Solver

• What: LLM + tools + planning (multi-step, uses output of step N as input to step N+1)
• The Key Concept: Context Engineering — the output of one step is shaped into precise input for the next
• Production example (coffee shop case):

Step 1: maps_tool("Mountain View", "SF") → "Millbrae"
Step 2: search_tool("good coffee in Millbrae")  <-- uses output from step 1

• Production use: Research agent, code review pipeline, document analysis workflows

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Level 3: The Collaborative Multi-Agent System

• What: A "Project Manager" agent + specialized sub-agents
• Why not one giant agent: Specialization. Each agent has a focused system prompt, relevant tools, and smaller context → cheaper, faster, more reliable
• Production example — Product Launch:

OrchestratorAgent --> MarketingAgent   (writes press release)
                  --> WebDevAgent      (builds landing page)
                  --> DataAgent        (pulls competitor analysis)

• Communication: Agents share state via session.state or A2A protocol

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Level 4: The Self-Evolving System

• What: System creates new tools or new agents on the fly when it detects a capability gap
• Production use: Very experimental. Research/internal automation. Not for customer-facing production yet.
• The key skill: Agent identifies "I don't have a tool for this" and generates one dynamically

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The Production Trap

WARNING

Building at Level 3 or 4 before you've validated Level 1. Most production failures come from over-engineering the agent architecture before the individual agent is proven to work reliably on its own task.

Start at the lowest level that solves the problem. Add complexity only when you hit a real limit.

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Recall Hook

Encyclopedia → Expert → Strategist → Manager → Self-Growing Org — pick your level before you write a line of code.

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Sources

• Google ADK Whitepaper: Introduction to Agents

Know a production example of each level? Add it here — real examples make this more useful.