Setup guide
How to use an AI agent in Claude
Three short walkthroughs — Claude.ai, Claude Desktop, Claude Code. Pick the one that matches your setup. About five minutes each.
Before you start
You need two things: a Claude account (Claude Pro at $20/month is the practical minimum for Projects + long system prompts) and the agent skill file (Markdown persona) you want to load. If you don't have one yet, browse the Rent an Agent catalog — every listing ships with the file plus a setup-guide PDF.
Brand new to AI agents? Start with the beginner's guide for the bigger picture before diving into Claude-specific setup.
~5 minutes
Claude.ai (web)
The most common setup. Works on any device with a browser, no install needed.
- 1
Open Claude.ai and click Projects
Sign in to claude.ai. In the left sidebar, click Projects. Click Create Project. Give it a name like 'Digital Elon' or whatever your agent is — this is the workspace where the agent will be active.
Projects requires Claude Pro ($20/month) or higher.
- 2
Open Custom Instructions
Inside the project, click Set custom instructions (right sidebar). A text area opens.
- 3
Paste the entire agent skill
Open the agent persona file you downloaded (Markdown, e.g. elon_v3.md). Select all and copy. Paste into the custom-instructions text area. Save.
Don't trim or summarize the file — paste the full Markdown.
- 4
Start a new chat inside the project
From the project page, click Start chat. The agent persona is now active for every conversation you start inside this project. Your existing Claude conversations outside the project are unaffected.
~5 minutes
Claude Desktop
Native macOS / Windows / Linux app. Shares Projects + chat history with Claude.ai web, so set it up once and it works in both.
- 1
Install Claude Desktop
Download Claude Desktop from claude.ai/download (macOS, Windows, and Linux). Install and sign in with the same account you use on claude.ai.
- 2
Create or open a Project
Click Projects in the left sidebar. Create a new project for the agent, just as you would in the web app — Claude Desktop and claude.ai share the same Projects data.
- 3
Paste the agent skill in Custom Instructions
Open project settings → Custom Instructions. Paste the full Markdown agent file. Save.
- 4
Use the project for every conversation with this agent
Switch to the project from the sidebar before starting a chat. The system prompt is loaded automatically. Your other Claude projects remain isolated.
~3 minutes
Claude Code (CLI)
For developers using Anthropic's command-line coding agent. Auto-loads a CLAUDE.md file from the repo root as a persistent system prompt.
- 1
Open the terminal in your repo
Navigate to the root of the project where you want the agent active. Claude Code reads a CLAUDE.md from the repo root and treats it as a persistent system prompt for every session in that directory.
- 2
Save the agent skill as CLAUDE.md
Copy the agent persona file (e.g. elon_v3.md) into the repo root and rename it CLAUDE.md. If a CLAUDE.md already exists, append the agent content under a clear divider or replace it depending on whether the existing file is load-bearing.
Tip: many projects already check CLAUDE.md into git so the team shares the persona.
- 3
Start Claude Code
Run `claude` in the terminal. Claude Code auto-loads CLAUDE.md as the system prompt for the session. Confirm the persona is active by asking 'who are you' — the agent identity should reply.
Common issues
The system prompt feels like it isn't loading
Ask the model who it is. The agent persona should respond with its name and role. If Claude responds as a generic assistant, the persona didn't load — re-check the Custom Instructions / CLAUDE.md content and confirm you saved.
The agent persona fades after a long conversation
Normal. The context window is finite and the system prompt loses weight as the chat grows. Start a new conversation inside the same project to reset, or send a short reminder message like "stay in your role."
The file is too long for the Custom Instructions field
Confirm you're on Claude Pro or higher — the free tier truncates aggressively. If you are on Pro and the file is still too long, the persona file may be unusually large (most are 4–15 KB). Trim non-essential sections like extended examples.
Frequently asked questions
Related
Setup guide
Use an AI agent in ChatGPT
The ChatGPT equivalent: Custom Instructions, Custom GPT builder, and the OpenAI API. Three short walkthroughs.
Read the guide →
Setup guide
Use an AI agent in Cursor
The Cursor equivalent: Project Rules (.cursor/rules/*.mdc), legacy .cursorrules, or global Rules for AI.
Read the guide →
Product
Digital Elon
The flagship Rent an Agent listing. First-principles strategic operator that follows these exact setup steps. $99 one-time.
See the listing →
Anthropic
Claude — official site
Sign up, pricing tiers, and Anthropic's own product documentation. Pro plan ($20/month) is the minimum for the workflows above.
Visit anthropic.com →
Need an agent skill to set up?
Every listing on Rent an Agent ships as a Markdown agent skill plus a setup-guide PDF. Drop it into Claude in 5 minutes and start working.
Browse agents →