---
title: Block Kit limits
description: Every limit Slack puts on Block Kit payloads, from blocks per message to text lengths, options per select and table sizes, with the Slack page each comes from.
sidebar:
  label: Limits
seo:
  title: "Slack Block Kit limits and character limits"
  description: "Every Slack Block Kit limit in one place: blocks per message, modal and Home tab, text and character limits per field, elements per actions block, options per select, table rows and columns."
search:
  keywords: [character limit, max length, maximum, block kit limits, too many blocks]
---

Slack's API rejects a payload that breaks one of these limits: `chat.postMessage` answers with an
error such as `invalid_blocks` or `msg_blocks_too_long`, and `views.open` with
`invalid_arguments`. Every number on this page comes from Slack's own
reference at [docs.slack.dev](https://docs.slack.dev/reference/block-kit), and each limit links to the page it comes from.
Limits Slack doesn't document are left out.

## What this package checks

`@nkootstra/block-kit` is a renderer, not a validator: it draws whatever payload you give it, even
one Slack would reject. A message with 60 blocks renders all 60. Check limits on your server before
you send a payload to Slack, or as your users type in an
[editor](/guides/block-kit-editor).

A few limits do change how the preview behaves, the same way they do in Slack's client:

| Limit                                       | What the renderer does                                                                                                         |
| ------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| 3 views in a modal stack                    | `views.push` past the third view does nothing and logs a console warning. See [Modals](/guides/modals#the-3-view-stack-limit). |
| `min_length` / `max_length` on a text input | Shows the characters left while typing, and blocks Submit with Slack's message. See [Validation](/guides/validation).          |
| `min_value` / `max_value` on a number input | Blocks Submit with Slack's message.                                                                                            |
| `max_selected_items` on a multi-select      | Stops adding items at the limit and shows "You can select up to N items."                                                      |
| `max_files` on a file input                 | Keeps the first `max_files` files picked (10 when unset).                                                                      |
| `page_size` on a data table                 | Not read: the table always shows 5 rows per page, Slack's default.                                                             |

## Surfaces

| What                                     | Limit                                                                                                                    |
| ---------------------------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| Blocks in a message                      | [50](https://docs.slack.dev/block-kit)                                                                                   |
| Blocks in a modal                        | [100](https://docs.slack.dev/reference/views/modal-views)                                                                |
| Blocks in a Home tab                     | [100](https://docs.slack.dev/reference/views/home-tab-views)                                                             |
| Modal `title`, `submit` and `close` text | [24 characters each](https://docs.slack.dev/reference/views/modal-views)                                                 |
| `private_metadata` on a view             | [3,000 characters](https://docs.slack.dev/reference/views/modal-views)                                                   |
| `callback_id` on a view                  | [255 characters](https://docs.slack.dev/reference/views/modal-views)                                                     |
| `external_id` on a view                  | [255 characters, unique across the team](https://docs.slack.dev/reference/methods/views.open)                            |
| Views in a modal stack                   | [3 (the first, plus 2 pushed)](https://docs.slack.dev/surfaces/modals)                                                   |
| Message `text`                           | [Truncated past 40,000 characters; Slack advises under 4,000](https://docs.slack.dev/reference/methods/chat.postMessage) |
| `markdown_text` on `chat.postMessage`    | [12,000 characters](https://docs.slack.dev/reference/methods/chat.postMessage)                                           |
| Attachments in a message                 | [100](https://docs.slack.dev/reference/methods/chat.postMessage)                                                         |
| Contact cards in a message               | [10](https://docs.slack.dev/reference/methods/chat.postMessage)                                                          |

## Blocks

Every block's `block_id` is limited to 255 characters, and should be unique for each message or
view and each update of it ([section block](https://docs.slack.dev/reference/block-kit/blocks/section-block), and the
same on each block's page).

| Block                                              | What                                                              | Limit                                                                                                   |
| -------------------------------------------------- | ----------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------- |
| [`actions`](/blocks/actions)                       | `elements`                                                        | [25](https://docs.slack.dev/reference/block-kit/blocks/actions-block)                                   |
| [`alert`](/blocks/alert)                           | `text`                                                            | [200 characters](https://docs.slack.dev/reference/block-kit/blocks/alert-block)                         |
| [`card`](/blocks/card)                             | `title`, `subtitle`                                               | [150 characters each](https://docs.slack.dev/reference/block-kit/blocks/card-block)                     |
| [`card`](/blocks/card)                             | `body`, `subtext`                                                 | [200 characters each](https://docs.slack.dev/reference/block-kit/blocks/card-block)                     |
| [`card`](/blocks/card)                             | Buttons in `actions`                                              | [3](https://docs.slack.dev/reference/block-kit/blocks/card-block)                                       |
| [`card`](/blocks/card)                             | `hero_image` and `icon` URL; their `alt_text`                     | [3,000 characters; 2,000 characters](https://docs.slack.dev/reference/block-kit/blocks/card-block)      |
| [`carousel`](/blocks/carousel)                     | Cards                                                             | [1 to 10](https://docs.slack.dev/reference/block-kit/blocks/carousel-block)                             |
| [`container`](/blocks/container)                   | `title`, `subtitle`                                               | [150 characters each](https://docs.slack.dev/reference/block-kit/blocks/container-block)                |
| [`container`](/blocks/container)                   | `child_blocks`                                                    | [10](https://docs.slack.dev/reference/block-kit/blocks/container-block)                                 |
| [`container`](/blocks/container)                   | `icon` URL; its `alt_text`                                        | [3,000 characters; 2,000 characters](https://docs.slack.dev/reference/block-kit/blocks/container-block) |
| [`context`](/blocks/context)                       | `elements`                                                        | [10](https://docs.slack.dev/reference/block-kit/blocks/context-block)                                   |
| [`context_actions`](/blocks/context-actions)       | `elements`                                                        | [5](https://docs.slack.dev/reference/block-kit/blocks/context-actions-block)                            |
| [`data_table`](/blocks/data-table)                 | `rows`, header included                                           | [2 to 201](https://docs.slack.dev/reference/block-kit/blocks/data-table-block)                          |
| [`data_table`](/blocks/data-table)                 | Columns                                                           | [1 to 20](https://docs.slack.dev/reference/block-kit/blocks/data-table-block)                           |
| [`data_table`](/blocks/data-table)                 | Characters across all cells, per table and per message            | [20,000](https://docs.slack.dev/reference/block-kit/blocks/data-table-block)                            |
| [`data_table`](/blocks/data-table)                 | `page_size`                                                       | [1 to 100, default 5](https://docs.slack.dev/reference/block-kit/blocks/data-table-block)               |
| [`data_visualization`](/blocks/data-visualization) | Blocks in a message                                               | [2](https://docs.slack.dev/reference/block-kit/blocks/data-visualization-block)                         |
| [`data_visualization`](/blocks/data-visualization) | `title`, `x_label`, `y_label`                                     | [50 characters each](https://docs.slack.dev/reference/block-kit/blocks/data-visualization-block)        |
| [`data_visualization`](/blocks/data-visualization) | Series in a bar, line or area chart; segments in a pie            | [1 to 12](https://docs.slack.dev/reference/block-kit/blocks/data-visualization-block)                   |
| [`data_visualization`](/blocks/data-visualization) | Data points in a series                                           | [1 to 20](https://docs.slack.dev/reference/block-kit/blocks/data-visualization-block)                   |
| [`data_visualization`](/blocks/data-visualization) | Series `name`, segment `label`, data point `label`, each category | [20 characters each](https://docs.slack.dev/reference/block-kit/blocks/data-visualization-block)        |
| [`header`](/blocks/header)                         | `text`                                                            | [150 characters](https://docs.slack.dev/reference/block-kit/blocks/header-block)                        |
| [`image`](/blocks/image)                           | `image_url`                                                       | [3,000 characters](https://docs.slack.dev/reference/block-kit/blocks/image-block)                       |
| [`image`](/blocks/image)                           | `alt_text`; `title` text                                          | [2,000 characters each](https://docs.slack.dev/reference/block-kit/blocks/image-block)                  |
| [`image`](/blocks/image)                           | File types                                                        | [`png`, `jpg`, `jpeg`, `gif`](https://docs.slack.dev/reference/block-kit/blocks/image-block)            |
| [`input`](/blocks/input)                           | `label`, `hint`                                                   | [2,000 characters each](https://docs.slack.dev/reference/block-kit/blocks/input-block)                  |
| [`markdown`](/blocks/markdown)                     | `text`, across all `markdown` blocks in a payload                 | [12,000 characters](https://docs.slack.dev/reference/block-kit/blocks/markdown-block)                   |
| [`plan`](/blocks/plan)                             | Tasks                                                             | [50](https://docs.slack.dev/reference/block-kit/blocks/plan-block)                                      |
| [`section`](/blocks/section)                       | `text`                                                            | [1 to 3,000 characters](https://docs.slack.dev/reference/block-kit/blocks/section-block)                |
| [`section`](/blocks/section)                       | `fields`; each field's text                                       | [10; 2,000 characters](https://docs.slack.dev/reference/block-kit/blocks/section-block)                 |
| [`table`](/blocks/table)                           | `rows`                                                            | [100](https://docs.slack.dev/reference/block-kit/blocks/table-block)                                    |
| [`table`](/blocks/table)                           | Cells in a row; `column_settings`                                 | [20 each](https://docs.slack.dev/reference/block-kit/blocks/table-block)                                |
| [`table`](/blocks/table)                           | Characters across all cells, per table and per message            | [10,000](https://docs.slack.dev/reference/block-kit/blocks/table-block)                                 |
| [`video`](/blocks/video)                           | `title` and `description` text                                    | [Under 200 characters each](https://docs.slack.dev/reference/block-kit/blocks/video-block)              |
| [`video`](/blocks/video)                           | `author_name`                                                     | [Under 50 characters](https://docs.slack.dev/reference/block-kit/blocks/video-block)                    |

Slack's image block page lists the supported file types but no maximum file size or pixel
dimensions, so none are given here.

## Elements

Every interactive element's `action_id` is limited to 255 characters, and should be unique among
the `action_id`s in its block ([button element](https://docs.slack.dev/reference/block-kit/block-elements/button-element),
and the same on each element's page).

| Element                                          | What                                        | Limit                                                                                                                         |
| ------------------------------------------------ | ------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------- |
| [`button`](/elements/button)                     | `text`                                      | [75 characters; may truncate around 30](https://docs.slack.dev/reference/block-kit/block-elements/button-element)             |
| [`button`](/elements/button)                     | `value`                                     | [2,000 characters](https://docs.slack.dev/reference/block-kit/block-elements/button-element)                                  |
| [`button`](/elements/button)                     | `url`                                       | [3,000 characters](https://docs.slack.dev/reference/block-kit/block-elements/button-element)                                  |
| [`button`](/elements/button)                     | `accessibility_label`                       | [75 characters](https://docs.slack.dev/reference/block-kit/block-elements/button-element)                                     |
| [`checkboxes`](/elements/checkboxes)             | `options`                                   | [10](https://docs.slack.dev/reference/block-kit/block-elements/checkboxes-element)                                            |
| [`radio_buttons`](/elements/radio-buttons)       | `options`                                   | [10](https://docs.slack.dev/reference/block-kit/block-elements/radio-button-group-element)                                    |
| [`overflow`](/elements/overflow)                 | `options`                                   | [5](https://docs.slack.dev/reference/block-kit/block-elements/overflow-menu-element)                                          |
| [Select menus](/elements/select-menus)           | `options`                                   | [100](https://docs.slack.dev/reference/block-kit/block-elements/select-menu-element)                                          |
| [Select menus](/elements/select-menus)           | `option_groups`; options in each group      | [100; 100](https://docs.slack.dev/reference/block-kit/block-elements/select-menu-element)                                     |
| [Multi-select menus](/elements/select-menus)     | `options`; `option_groups`                  | [100; 100](https://docs.slack.dev/reference/block-kit/block-elements/multi-select-menu-element)                               |
| [Multi-select menus](/elements/select-menus)     | `max_selected_items`                        | [At least 1](https://docs.slack.dev/reference/block-kit/block-elements/multi-select-menu-element)                             |
| [`plain_text_input`](/elements/text-inputs)      | `min_length`                                | [0 to 3,000](https://docs.slack.dev/reference/block-kit/block-elements/plain-text-input-element)                              |
| [`plain_text_input`](/elements/text-inputs)      | `max_length`                                | [1 to 3,000](https://docs.slack.dev/reference/block-kit/block-elements/plain-text-input-element)                              |
| [`rich_text_input`](/elements/rich-text-input)   | `min_lines`, `max_lines`                    | [1 to 100 each; `max_lines` defaults to 8](https://docs.slack.dev/reference/block-kit/block-elements/rich-text-input-element) |
| [`file_input`](/elements/file-input)             | `max_files`                                 | [1 to 10, default 10](https://docs.slack.dev/reference/block-kit/block-elements/file-input-element)                           |
| [`file_input`](/elements/file-input)             | File size                                   | [100 MB](https://docs.slack.dev/reference/block-kit/block-elements/file-input-element)                                        |
| [`image`](/elements/image-element)               | `image_url`                                 | [3,000 characters](https://docs.slack.dev/reference/block-kit/block-elements/image-element)                                   |
| [`workflow_button`](/elements/workflow-button)   | `text`; `accessibility_label`               | [75 characters each](https://docs.slack.dev/reference/block-kit/block-elements/workflow-button-element)                       |
| [`feedback_buttons`](/elements/feedback-buttons) | Each button's `text`; `accessibility_label` | [75 characters each](https://docs.slack.dev/reference/block-kit/block-elements/feedback-buttons-element)                      |
| [`feedback_buttons`](/elements/feedback-buttons) | Each button's `value`                       | [2,000 characters](https://docs.slack.dev/reference/block-kit/block-elements/feedback-buttons-element)                        |
| [`icon_button`](/elements/icon-button)           | `value`; `accessibility_label`              | [2,000 characters; 75 characters](https://docs.slack.dev/reference/block-kit/block-elements/icon-button-element)              |

### Placeholders

The `placeholder` text on a select menu, multi-select menu, date picker, time picker,
`plain_text_input`, `email_text_input`, `url_text_input`, `number_input` and `rich_text_input` is
limited to 150 characters each (see each element's page, for example the
[select menu element](https://docs.slack.dev/reference/block-kit/block-elements/select-menu-element)).

## Composition objects

| Object                                                | What                        | Limit                                                                                                           |
| ----------------------------------------------------- | --------------------------- | --------------------------------------------------------------------------------------------------------------- |
| Text object                                           | `text`                      | [1 to 3,000 characters](https://docs.slack.dev/reference/block-kit/composition-objects/text-object)             |
| Option                                                | `text`, `description`       | [75 characters each](https://docs.slack.dev/reference/block-kit/composition-objects/option-object)              |
| Option                                                | `value`                     | [150 characters](https://docs.slack.dev/reference/block-kit/composition-objects/option-object)                  |
| Option                                                | `url` (overflow menus only) | [3,000 characters](https://docs.slack.dev/reference/block-kit/composition-objects/option-object)                |
| Option group                                          | `label`                     | [75 characters](https://docs.slack.dev/reference/block-kit/composition-objects/option-group-object)             |
| Option group                                          | `options`                   | [100](https://docs.slack.dev/reference/block-kit/composition-objects/option-group-object)                       |
| [Confirmation dialog](/elements/confirmation-dialogs) | `title`                     | [100 characters](https://docs.slack.dev/reference/block-kit/composition-objects/confirmation-dialog-object)     |
| [Confirmation dialog](/elements/confirmation-dialogs) | `text`                      | [300 characters](https://docs.slack.dev/reference/block-kit/composition-objects/confirmation-dialog-object)     |
| [Confirmation dialog](/elements/confirmation-dialogs) | `confirm`, `deny`           | [30 characters each](https://docs.slack.dev/reference/block-kit/composition-objects/confirmation-dialog-object) |

## Related

**[Validation](/guides/validation)**

The checks Slack's client runs on a modal before it sends `view_submission`.

**[Blocks](/blocks)**

Every block type, with its fields and live examples.

**[Block Kit editor](/guides/block-kit-editor)**

Let your users edit a payload and see the Slack preview update as they type.

**[Examples](/examples)**

Complete payloads for common messages, modals and Home tabs.