Understanding Agent and Skill in One Diagram

What is an Agent?

• LLM = the brain
• Agent System = the body
• LLM Credit = oxygen
  • No payment, LLM stops = no oxygen, brain dies
• Tool Call = hands, feet, and senses
  • Eyes that see (gather information, e.g. web search)
  • Hands that write (produce output, e.g. edit files)

What is a Skill?

An abstracted SOP.

For example:

• Making a drink
  • Grab a cup (restock if there are none left)
  • Pour the tea (match the tea to the drink order)
  • Add sugar (how much?)
  • Add ice (how much?)
  • Seal the cup
  • Hand it to the customer
• Taking a shot on goal
  • Eyes (Tool Call) locate the goal frame and the goalkeeper’s position
  • Pass that information to the brain and think through the best way to shoot (call LLM)
  • The body (Agent System) uses nerves to control the foot (Tool Call) to take the shot

What are Scripts, CLIs, and MCP Tools?

SOPs with clear enough steps aren’t a good fit for a Skill (markdown) — they’re better packaged directly as a script. More complex flows get packaged into a CLI or MCP Tool.

Level	Definition	Human-era equivalent	Packaged as today
Script	Fully automatic, no input needed	Factory worker tallying on abacus	Counting sensor, auto-accumulates
CLI	Takes a command, processes it, returns a fixed result	Cashier manually ringing up items	POS machine (enter items → auto-calculate and print receipt)
MCP Tool	Connects to external services, standardized communication	Calling a courier company	Integrating a delivery API

With both a process (Skill) and the right tools (Script, CLI, MCP Tool), handling any SOP becomes far more efficient. For example:

• Taking a customer’s order (Skill)
  • Ask what they’d like and confirm the order
  • Operate the POS machine — enter the order and calculate the total (CLI)
  • Collect payment and give change
  • Operate the POS machine — check out, print the receipt and invoice (CLI)
  • Hand the invoice to the customer

What are MCP and MCP Tools?

Think of a remote control (MCP) and an air conditioner (MCP Tool).

• Remote control = MCP
  • The standardized interface an Agent uses to communicate with external services
  • The remote doesn’t cool the room — it just sends commands
• Air conditioner = MCP Tool
  • The external service that actually does the work
  • It only acts once it receives a command

The upside: one remote control standard can operate the AC, the TV, and the sound system. One MCP standard lets an Agent connect to a delivery API, a weather API, Slack, and more — without learning a new communication protocol for every service.

Summary

Humans actually work the same way — things we do repeatedly long enough become instinct, habit (Script). What’s left — the things that need actual thought and judgment — is when we engage the brain (Skill).

Agents just take that same idea and move it into software.