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

# Create and update formulas as an agent

Use `write_formulas` only when the user wants a persistent model change.

## Workflow

1. Resolve the target and referenced properties.
2. Identify the scenario.
3. Determine formula scope from explicit context or a table block.
4. Read formulas at the exact condition to determine create versus update.
5. Validate the expression and condition.
6. Write the formula.
7. Review applied and rejected results.
8. Verify calculated values when the change is material.

## Create versus update

Call `list_formulas` with the final condition.

* If a matching formula exists, pass its `formula_id` to update it.
* If none exists, omit `formula_id` to create a new formula.

## Batch behavior

`write_formulas` accepts several formula items.

* `partial` is the default. Valid items are applied and invalid items are rejected.
* `atomic` rejects the entire batch when any item is invalid.

Inspect the attempted, applied, and rejected counts. Never imply that all items were written when the result reports a partial apply.

## Required fields

Each item requires:

* `property_id`
* `condition`
* `expression`

Use `formula_break_id` only for a Date-scoped Formula-period formula.

## Response behavior

Written formulas render as cards. Do not restate each formula in prose. Send a one-sentence headline, disclose assumptions, and ask a focused follow-up only when needed.