> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base44.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom instructions

> Give the agent app-specific instructions.

Custom instructions are free text instructions stored at the app level and sent to Base44's agent on every [turn](/developers/white-label/the-build-turn). Unlike the [design system](/developers/white-label/design-system), [skills](/developers/white-label/skills-and-mcp#skills), and [MCP connections](/developers/white-label/skills-and-mcp#mcp-servers), which apply to everything built in your workspace, custom instructions belong to a single app.

Use custom instructions to tell the agent:

* How the specific app fits into your platform
* How to [connect back to your platform](#connect-back-to-your-platform), to access user data or call your APIs
* Invoke a [skill](/developers/white-label/skills-and-mcp#skills) on your builders' behalf

## Set custom instructions

Set custom instructions using the `custom_instructions` field when creating an app by calling [Create app](/developers/white-label/the-build-turn). You cannot add custom instructions to an app after it's already created.

The instructions are sent to the agent on each [turn](/developers/white-label/the-build-turn) when building the app. Only the first 10,000 characters are sent. Longer text is stored in full but silently cut off in the prompt.

## Connect back to your platform

When you use custom instructions to connect an app back to your platform, be explicit about how the integration should work.

For example, specify:

* Which entities hold which data
* Their row-level security rules
* Which API calls are allowed
* What should be read-only

## See also

* [Setup checklist](/developers/white-label/setup-checklist): Everything you need to do to get an integration running
* [The build turn](/developers/white-label/the-build-turn): The loop your product wraps
* [Design system](/developers/white-label/design-system): What every app your builders build looks like
* [Skills and MCP](/developers/white-label/skills-and-mcp): What the agent knows while it builds, and what it can call