Guide
How to build your own AI agent without coding
Short answer
Start with one file. A Carrierfile can already hold an agent: its name, its identity, how it works with you, and its memory. It’s free and works in any AI. When your agent outgrows one file, give it a castle: a folder linked to your Claude or ChatGPT desktop app, where the file grows into its own systems and subfolders. A castle needs an entry-level paid plan, about $20 a month. The first lesson of Castle Blocks is free.
Step one: an agent in a single file
Every Carrierfile has a section called The Agent. You give your AI a name, and the first time you type unpack, it writes and signs its own identity in its own words.
Alongside that, the file holds who you are, how you work together, your projects, named tones, a growing set of memories, and a session log.
That’s already an agent: a named collaborator that remembers you and picks up where you left off, in any AI, on any plan, including free ones. Build yours in about five minutes.
Step two: when one file isn’t enough
A single file has limits. As your agent takes on more projects and more memories, everything competes for space in one document. At some point it needs room to spread out.
That’s a castle: a folder on your computer, linked to your Claude or ChatGPT desktop app. It starts as one folder with one file in it, and grows one block at a time, so you understand every piece. What used to live in one file gets broken out into systems and subfolders, and the agent lives in the castle and manages the projects inside it. A grown castle has:
- A Carrierfile at the center. It doesn’t go away. It becomes the entry point the agent reads first: its identity and how the castle works.
- Files of their own for you and for the agent: who you are, who the agent is, and how it’s tuned.
- A status file and a session log, so every session picks up where the last one left off.
- Rooms for your projects, each with its own context.
- A memory folder, where old sessions are composted into short notes the agent can search.
| Carrierfile | Castle | |
|---|---|---|
| Shape | One plain-text file | A folder of files and subfolders |
| Holds an agent | Yes: name, identity, memory, tones | Yes, with room to grow into separate systems |
| Projects | Listed in the file | Each in its own space; the agent manages them |
| How you use it | Paste it into any chat, type “unpack” | Link the folder to your Claude or ChatGPT app and work there |
| Size | Stays small by design | Grows with your work, with a Carrierfile at its center |
| What you need | Any AI, any plan, including free | An entry-level Claude or ChatGPT plan (about $20 a month) |
| Coding | None | None |
What you need for a castle
- A computer with the Claude or ChatGPT desktop app.
- A regular entry-level plan for Claude or ChatGPT, about $20 a month. That level lets you link a folder on your computer to the app, which is what lets your agent keep its own files and manage your projects. Free chat plans can’t do that.
- An empty folder for the castle. The lessons call it
CarrierfileCastle. - 10 to 20 minutes for the first lesson, and an idea for your agent’s name.
- No coding. You build it in plain language, one step at a time.
No developer tools, servers, or expensive tiers. The castle runs on the same plan many people already pay for. Because it’s all plain files in a folder you own, you can read every word, back it up, and move it.
How to start
- Break ground. Make an empty
CarrierfileCastlefolder and link it in your Claude or ChatGPT desktop app. Castle Blocks, lesson 1: Groundbreaking is free. One folder, one file, one name: your AI sends you to the builder to make your Carrierfile, then becomes your agent and writes and signs its own identity. - Keep building. Each block builds on the last. Block 2, Tuning, shapes how your agent acts and speaks. The full series is part of a paid subscription to The Carrierfile on Substack.
- Not ready for a castle? Just build a Carrierfile and paste it into any chat. It’s free, and it’s the same file you’ll bring to a castle later.
Who this is for
Castle Blocks is written by Anna Sutton and her own agent, Calcifer, who started in a single Carrierfile and now lives in a castle. It’s written for non-technical people and anyone who likes to learn through play. If you’ve felt that AI tools were built for someone else, this is for you.
Questions people ask
Can I build an AI agent for free?
Yes. A Carrierfile can hold an agent, with its name, identity, working style, and memory, in one plain-text file. It is free and works in any AI on any plan, including free ones.
Do I need to know how to code to build an AI agent?
No. Both a Carrierfile and a castle are built in plain language, step by step. No programming is involved.
What is the difference between a Carrierfile and a castle?
A Carrierfile holds your agent and its memory in one file you paste into any AI. A castle is a folder linked to your Claude or ChatGPT app where that agent can spread out, with its memory, identity, rituals, and projects broken out into their own systems and subfolders. A Carrierfile stays at the center of every castle.
When should I move from a Carrierfile to a castle?
Whenever you want. A castle starts as one folder with one Carrierfile in it, so you can begin right away, or keep using a single file until your agent outgrows it: lots of projects, lots of memories, or you want it to manage files for you.
How much does a castle cost?
The first Castle Blocks lesson is free. A castle needs a regular entry-level Claude or ChatGPT plan, about $20 a month, so the app can link to a folder on your computer. The full Castle Blocks series is part of a paid Substack subscription.
Is my agent locked to one AI company?
No. A castle is plain files in a folder you own, and your Carrierfile can travel: take a copy to any other AI, work there, pack up, and bring it home, where your agent runs a health check before anything comes back in.
Start your agent free. Build a Carrierfile and give your agent a name. Ready for a castle? The first lesson of Castle Blocks is free and takes 10 to 20 minutes.
Build your Carrierfile →Ready for a castle? Castle Blocks, lesson 1 (free) →