> ## Documentation Index
> Fetch the complete documentation index at: https://docs.beam.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Variable Fill
> Configure how each tool input receives a value while an agent flow runs.
Variables control how data moves through an agent flow. For every input variable on a node, choose the fill method that supplies its value at runtime.
Fill methods
Beam provides seven fill methods:
AI fills the value automatically.
AI fills the value from the description you provide.
Uses an output from another tool in the flow.
Uses a fixed value that you enter manually.
Prompts the user to provide the value at runtime.
Looks up the value from the agent's memory.
Extracts the value from a task attachment.
1. Open the agent's **Flow**.
2. Select the node that needs the input.
3. In the node sidebar, open **Parameters**.
4. Under **Input variables**, select the variable's current fill method.
5. Choose the fill method that matches the source of the value.
Choose the right fill method
| If the value... | Use |
| ------------------------------------------------- | --------------- |
| Should be produced automatically by AI | Auto fill |
| Needs instructions that tell AI how to produce it | Prompt fill |
| Comes from an earlier tool output | Linked fill |
| Is fixed for every execution | Static fill |
| Must be supplied by a user during execution | User fill |
| Should be looked up in the agent's memory | Memory fill |
| Comes from a task attachment | Attachment fill |
How each fill method works
Auto fill
Use Auto fill when Beam can determine the value without an explicit instruction. The node fills the value automatically from the available execution context.
Prompt fill
Use Prompt fill when the node needs your instructions for how to produce the value. Write a clear description of the required value and format in the variable's value field.
Linked fill
Use Linked fill to pass an earlier node's output to a later node. The source node must run before the node that consumes the linked value.
Static fill
Use Static fill for a value you enter once and want to keep the same for every execution, such as a fixed identifier or configuration value.
User fill
Use User fill when the person running the task must provide the value at runtime.
Memory fill
Use Memory fill when a node needs knowledge from the agent's Memory module. Add documents in **Configuration → Memory**, then use Memory fill to look up a value from that knowledge base. See [Core Concepts](/01-getting-started/core-concepts/core-concepts#memory) for how agent memory works.
Attachment fill
Use Attachment fill when the node needs to extract a value from a file attached to the task.
Next steps
Choose and configure tools for your agent.
Build a flow with tools, conditions, and triggers.
Configure integration-specific variable patterns and connectors.
Build custom API connections for advanced integration patterns.