> For the complete documentation index, see [llms.txt](https://docs.feathery.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.feathery.io/platform/build-forms/advanced-logic/visual-rule-builder/set-field-value-action.md). # Set Field Value Action A set field action requires the selection of a form field and a "value" that will be set into the field. The "value" can be either: * A specific value that may be a number, some text, true/false, etc. * An expression that combines specific values and/or fields using arithmetic/text/logic operators and optionally parenthesis. To support the above possibilities, set field actions support both a value entry "mode" and an expression entry "mode". Set field actions will always start in value entry mode. In value entry mode you may simply enter a number or text or if the field is a select type field, select one of the select options.

The set field actions have an overflow menu (3-dot icon) that has an option to put the input into expression input mode (see above). In expression input mode, enter specific values and/or select fields and combine them with operators and parenthesis as needed. Here are some very simple examples:

Example Rule Builder Expression combining text

## Expression Operators The following operators are supported in expressions. Parenthesis are also supported for numeric expressions. | Operator | Name | Purpose | Example | | -------- | --------------------- | ----------------------------------------------------- | -------------------------- | | + | Addition | Add two numeric sub-expressions | a + b | | - | Subtraction | Subtract two numeric sub-expressions | a - b | | \* | Multiplication | Multiply two numeric sub-expressions | a \* b | | / | Division | Divide two numeric sub-expressions | a / b | | + | Concatenation | Concatenate two text sub-expressions | firstName + " " + lastName | | ==, === | Equality | Compare two sub-expressions for equality | a == b | | !=, !== | Inequality | Compare two sub-expressions for inequality | a !== b | | > | Greater than | Compare two sub-expressions for greater than | a > b | | >= | Greater than or equal | Compare two sub-expressions for greater than or equal | a >= b | | < | Less than | Compare two sub-expressions for less than | a < b | | <= | Less than or equal | Compare two sub-expressions for less than or equal | a <= b | --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.feathery.io/platform/build-forms/advanced-logic/visual-rule-builder/set-field-value-action.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.