Picking the Right Primitive
Decide tool vs resource vs prompt for a feature.
Picking the Right Primitive is a free MCP Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the MCP Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Three Choices, One Question
You know tools, resources, and prompts. Now the skill is choosing the right one for each feature you want to expose. 🧭
Who Is in Control?
The clearest divider is control. Tools are model-controlled, resources are application-controlled, and prompts are user-controlled.
Does It Take Action?
If a feature does something, like sending mail or writing a row, it is almost always a tool. Action is the tool's signature trait.
Is It Just Information?
If the model only needs to read something, a file, record, or setting, reach for a resource. No side effects, just context.
Is It a Saved Way to Ask?
If you want a one click, repeatable way to start a task, that is a prompt. The user triggers it and fills in a few inputs.
Weather: Tool or Resource?
Fetching live weather usually fits a tool, since the model decides when it needs fresh data and passes a city argument.
A README: Resource
Your project's README is static context the AI should see. That is a textbook resource, attached by the app, not run by the model.
Summarize This: Prompt
A reusable summarize this command the user picks from a menu is a prompt. It templates the instruction so every summary starts the same way.
They Work Together
Real servers combine all three: a resource feeds context, a prompt frames the request, and a tool carries out the resulting action.
When in Doubt
Unsure between tool and resource? Ask whether it changes anything. If yes, it is a tool; if it only informs, it is a resource.
Map Features to Primitives
Before coding, list each feature and tag it tool, resource, or prompt. That quick mapping keeps your server clean and predictable.
Quick Check
Pick the right primitive for this case.
Recap: Choosing Wisely
Well done! Ask who controls it and whether it acts: tool for actions, resource for read-only data, prompt for saved requests. ✅
Frequently asked questions
Is the “Picking the Right Primitive” lesson free?
Yes — the full text of “Picking the Right Primitive” is free to read here on the web, and the MCP Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the MCP Academy course, upgrade to CoddyKit PRO.
What will I learn in “Picking the Right Primitive”?
Decide tool vs resource vs prompt for a feature. You practise MCP Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start MCP Academy?
No prior experience is required. MCP Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Picking the Right Primitive” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this MCP Academy lesson?
Yes. Every MCP Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Tools: Actions the Model Takes
- Resources: Data the Model Reads
- Prompts: Reusable Instructions
- Picking the Right Primitive