> ## Documentation Index
> Fetch the complete documentation index at: https://c42d5cb-opencomputer.manicule.dev/llms.txt
> Use this file to discover all available pages before exploring further.
> For every page in one file, fetch https://c42d5cb-opencomputer.manicule.dev/llms-full.txt (large).
> To search and read these docs as tools, connect the MCP server at https://c42d5cb-opencomputer.manicule.dev/api/mcp.
> Every agent surface: https://c42d5cb-opencomputer.manicule.dev/.well-known/llms-manifest.json

# Files and cards (/slack/files-and-cards)

<!-- agent-signals: reading_time_min: 2 · est_tokens: 992 · updated: 2026-11-12 -->
Related: [Threads](/slack/threads.md), [Shared threads](/slack/shared-threads.md), [Linked and spawned threads](/slack/linked-and-spawned-threads.md), [Mid-turn messages](/slack/mid-turn-messages.md), [Permission modes](/slack/permission-modes.md), [Approvals, questions and plans](/slack/approvals-questions-plans.md)

> Attachments up to 1 GiB reach the session as file paths; the session posts files and cards back with `send_file` and `post_card`

<Frame>
  <img src="/_assets/a9da12873b5ac657f7d0eaeb10cbf329ea8aef99758ab184dd0d9f914fd64450" alt="A PNG posted by the session into its thread, shown inline under its comment and file name" width="1552" height="1334" />
</Frame>

## Files into a session

Attach files to a message addressed to `@computer`. The runner downloads each one to a temp directory on the computer, outside the repositories, and gives the model the path.

| File              | What happens                                                                                                 |
| ----------------- | ------------------------------------------------------------------------------------------------------------ |
| 5 MiB or smaller  | Downloaded before the message reaches the model. PNG, JPEG, GIF and WebP are also given to the model inline. |
| Larger than 5 MiB | The message is delivered at once; the file appears at the path when its background download completes.       |
| Larger than 1 GiB | Not downloaded.                                                                                              |
| Download failed   | The model gets `[attached <name>: could not be downloaded (<reason>)]`.                                      |

A reason that mentions an HTML page means the bot is missing the `files:read` scope; see [Connect Slack](/self-hosting/gateway).

## Files out of a session

The session posts a file into its thread with the `send_file` tool. PNG, JPEG, GIF and WebP images render inline; any other file is an attachment.

A script running in the session can post without a tool call. It exits 0 when the file is posted; otherwise it prints the reason to stderr and exits 1.

```bash
calvin-send-file <path> [comment words...] [--title T] [--alt TEXT]
```

| Limit            | Value                                                                                                                                         |
| ---------------- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| Location         | Inside the session's working directory or the temp directory                                                                                  |
| Type and size    | A regular, non-empty file of at most 100 MiB                                                                                                  |
| Files per runner | 50. The count starts again when the runner does.                                                                                              |
| Secrets          | A file containing a session secret's value is refused; the refusal names the secret. See [Redaction](/slack/secrets-and-variables#redaction). |
| Slack scope      | `files:write`                                                                                                                                 |

## Cards

The session posts a table, a chart or a set of labelled fields as a Slack card with the `post_card` tool.

<Frame>
  <img src="/_assets/ed3672bc7b6be3a56911422f14c08d858be74d058e276b90120c9607681404e3" alt="A card in a thread: a title, four labelled fields, a table and a link button" width="1552" height="1282" />
</Frame>

| Limit            | Value                                 |
| ---------------- | ------------------------------------- |
| Tables per card  | 1, up to 100 rows and 20 columns      |
| Charts per card  | 2, each up to 12 series and 20 points |
| Fields per card  | 10                                    |
| Cards per runner | 50                                    |

* A card over a limit is refused, never posted in a reduced form.
* A card whose content includes a secret's value is not posted.
* Buttons on a card are links only; none sends a click back to the session.