What is an Agent?

Definition

An AI agent is a system that perceives its environment, reasons about it using a language model, and takes actions to achieve a goal — then observes the result and repeats.

More formally, an agent is characterized by:

1. Perception — receiving input (user prompt, observations from tools)
2. Reasoning — using an LLM to decide what to do next
3. Action — calling tools, writing code, browsing the web, etc.
4. Memory — keeping track of previous steps (short-term context)

The agent loop

while goal not achieved:
    thought  = LLM.think(context)
    action   = LLM.decide(thought)
    result   = tool.run(action)
    context += [thought, action, result]

Agents vs. simple LLM calls

Aspect	LLM call	Agent
Steps	Single	Multiple (loop)
Tools	None	Many
Memory	No	Short/long-term
Autonomy	Low	High

Notes

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