Skip to main content
When users submit a modal, you can send the form data to your backend and/or update the original Slack message. Use this for feedback, approvals with comments, and data entry workflows.

​
Prerequisites

​
Submission flow

  1. User fills the modal and clicks Submit
  2. LithoBlocks receives the submission and extracts form values
  3. You can trigger a webhook (POST form data to your API) and/or a message update (change the original message)
  4. Optional: show a confirmation or thank-you in the message

​
Submission data

Form values are sent as a structured object, for example: 
{
  "field_label_1": "value",
  "field_label_2": ["option1", "option2"],
  "field_label_3": "2024-12-25"
}
Field keys match your modal field labels or IDs; values are strings, arrays (multi-select), or formatted dates/times.

​
Configure submission actions

  1. Open your modal definition
  2. Under On submit, add one or both:
    • Webhook — Select a webhook destination; the payload will include the form data (and optional interaction placeholders)
    • Message update — Choose strategy (replace self, replace all, add response block) and define the new content
  3. Save the modal

​
Combined actions

You can run both a webhook and a message update on submit: e.g. POST data to your API and append ”✓ Submitted by [user] at [time]” to the original message.

​
Webhook usage in templates

Modal submission webhooks use the same webhook destinations as buttons. For advanced configuration — authentication, retries, payload templating, and monitoring — see Webhook destinations. To view and debug webhook delivery and responses, see Understanding logs.

​
Next steps

Modal basics

Create and configure modals.

Webhook destinations

Auth, retries, and advanced payload config.

Understanding logs

Debug webhook delivery and responses.