Custom instructions

Custom instructions are free text instructions stored at the app level and sent to Base44’s agent on every turn. Unlike the design system, skills, and MCP connections, 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, to access user data or call your APIs
• Invoke a skill on your builders’ behalf

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Set custom instructions

Set custom instructions using the custom_instructions field when creating an app by calling Create app. You cannot add custom instructions to an app after it’s already created. The instructions are sent to the agent on each 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.

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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

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See also

• Setup checklist: Everything you need to do to get an integration running
• The build turn: The loop your product wraps
• Design system: What every app your builders build looks like
• Skills and MCP: What the agent knows while it builds, and what it can call