# Keep an app's rules in one data file so the agent can change behavior without touching code

> A builder made a 90s-style scrolling cable TV guide for Plex, Jellyfin and Emby with Claude. A written spec came first, all channel and schedule rules live in one JSON file, and later ports used the first app as the reference.

- URL: https://paperchasewebb.ai/bots/marketplace/items/keep-an-app-s-rules-in-one-data-file-so-the-agent-can-change-behavior-without-touching-code/
- Type: Agent use case pack
- Category: Vibe coding
- By: PaperChaseWebb
- Works with: Claude Code, Claude (named in the listing); Plain .md
- Price: Free USD
- Difficulty: Intermediate
- Setup time: 30 min
- Time to result: One working session
- Format: Markdown (.md) file, keep-an-app-s-rules-in-one-data-file-so-the-agent-can-change-behavior-without-touching-code.md
- Version: 1.0, updated 2026-10-27
- License: Personal and commercial use. Credit the original source when you share the workflow.

## What you end up with

Putting rules in data gives the agent a small, safe surface to edit and gives you a single file to review.

## What you get

- A plain-language summary of the workflow
- A fill-in prompt template
- What to watch out for
- A link to the original source

## Who it is for

Builders who already use AI agents and want a proven workflow they can copy into their own project.

## Tools needed

- Claude: writes the app, the data scripts and each platform port
- TMDB API: metadata for building channels
- Plex, Jellyfin, Emby: the user's own media servers
- You need: An AI coding agent or chat model
- You need: A small real task to try it on

Cost to run: Free with the agent plan you already use.

## How it works

1. **Write a one-page spec before the first prompt.** Write a one-page spec before the first prompt Expected: Done before you move to the next step.
2. **Move every rule that might change into one data file with a schema.** Move every rule that might change into one data file with a schema Expected: Done before you move to the next step.
3. **Ask the agent to change behavior through the data file first, code sec.** Ask the agent to change behavior through the data file first, code second Expected: Done before you move to the next step.
4. **Test each build on the real device.** Test each build on the real device Expected: Done before you move to the next step.
5. **When porting, give the agent the working app and its tests as the spec.** When porting, give the agent the working app and its tests as the spec Expected: Done before you move to the next step.

## Sample prompt: Workflow template (Claude, TMDB API)

```
Apply this workflow to [your project]:
1. Write a one-page spec before the first prompt
2. Move every rule that might change into one data file with a schema
3. Ask the agent to change behavior through the data file first, code second
4. Test each build on the real device
5. When porting, give the agent the working app and its tests as the spec
Stop and ask me before anything irreversible: deploys, payments, sends or deletes.
```

Adapted by PaperChaseWebb. Not the original author's prompt.

## Free preview of keep-an-app-s-rules-in-one-data-file-so-the-agent-can-change-behavior-without-touching-code.md

````markdown
# Keep an app's rules in one data file so the agent can change behavior without touching code

PaperChase agent use case (free feed entry), version 1.0. Source: [u/chadMueller on r/ClaudeAI](https://www.reddit.com/r/ClaudeAI/comments/1xgts0i/i_built_a_90s_cable_tv_guide_for_plex_jellyfin/), 2026-10-27.

## What they did

The author wrote a spec for the guide before any code. Channel lineups, time slots and display rules sit in one JSON data file, so most changes are edits to data rather than code, and helper scripts pull metadata from TMDB to fill channels. Every build was tested on a real TV device, not only a simulator. Users suggest and vote on features in a Discord, which sets the backlog. When the app moved to a new platform, the existing app served as the spec for the port. The author reports more than 1,400 Apple TV downloads.

## Worth knowing

Putting rules in data gives the agent a small, safe surface to edit and gives you a single file to review. Using a working app as the spec for a port is more precise than describing it again in prose. Download figures are the author's own.
````

## Worth knowing

- Putting rules in data gives the agent a small, safe surface to edit and gives you a single file to review. Using a working app as the spec for a port is more precise than describing it again in prose. Download figures are the author's own.
- Figures are as reported by the original author and were not re-measured by us.

## Questions

**Where does this come from?** A public post credited to u/chadMueller on r/ClaudeAI. Source: https://www.reddit.com/r/ClaudeAI/comments/1xgts0i/i_built_a_90s_cable_tv_guide_for_plex_jellyfin/

**Is it free?** Yes. Feed entries are free to read and download.

## How to get it

Free sample. Download it directly at https://paperchasewebb.ai/bots/marketplace/items/keep-an-app-s-rules-in-one-data-file-so-the-agent-can-change-behavior-without-touching-code/, no signup.

Seller: PaperChaseWebb Inc., mgmt@paperchasewebb.com