Guide
How to share an HTML or Markdown file in Slack
Updated 30 October 2026
Slack keeps an uploaded .html or .md file as a file, not a page. To see the page, a reader downloads it and opens it in a browser, and on a phone Slack downloads only images. Post a link instead: publish the file on ashare.net for your company’s email domain or for specific emails, paste the link in the channel, and readers open the page in their browser after signing in with a code from their email.
What Slack does with an HTML or Markdown file
You can add files up to 1 GB to a conversation, and Slack scans each one for malware. Slack’s API names an uploaded .html file “HTML” and a .md file “Markdown (raw)”. Slack’s help describes inline previews for images and Office files; it says nothing about rendering a web page or formatting a Markdown file.
So the file sits in the channel as an attachment. On desktop a reader downloads it and opens it in a browser. On a phone that step fails: Slack’s help says that on mobile you can only download image files.
A downloaded file also brings the usual problems of attachments. Each reader has their own copy, a fix means posting a new file and hoping people open the newer one, and you can’t tell who looked at it.
Options inside Slack
A snippet, to show the source
A snippet holds text with a file type for syntax highlighting. Others can download it, view the raw version or comment on it. That is good for reviewing the HTML code itself, not for reading the page it produces.
A canvas, for a Markdown note
Canvases are documents inside Slack. Their API creates a canvas from Markdown, with headings, lists, tables and code blocks; Markdown is the only content type it takes, so this route is for .md, not .html. For a short Markdown note meant for one channel, a canvas keeps it readable without leaving Slack.
Slack Code, for agent work started in Slack
Slack Code is rolling out gradually. An approved agent opens a temporary code channel, and its artifacts there include an HTML view: live HTML for prototypes, presentations or previews. If your workspace has it and the work starts in that channel, the page stays in Slack. Code channels leave the sidebar after seven days without activity.
What each way gives the reader
| Way | What the reader sees | Fits |
|---|---|---|
| Upload the .html or .md file | A file to download; the page only after opening it from disk, on desktop | Sending the file itself to someone who will edit it |
| Snippet | The source, highlighted | Code review of the HTML |
| Canvas | Formatted text inside Slack | A short Markdown note |
| Slack Code HTML view | Live HTML in a code channel | Agent work started in Slack, where it’s available |
| A link to ashare.net | The page in the browser, on desktop or phone | Reports, specs and dashboards for people you choose |
Post a link instead of the file
- Publish the file. Upload the .html or .md file, or a ZIP of a small site with
index.html, on My documents. Or ask your agent to publish it: Claude Code, Codex, Cursor, ChatGPT and other clients connect over MCP. Markdown is rendered as a formatted page. - Choose who opens it. A new document is private. Under Access, pick Company to open it to everyone who signs in with an email on your company’s domain, add specific people by email (up to 100), or make it public with a password and an expiry.
- Paste the link in Slack. A reader clicks it, the page opens in the browser, and they type their email and a 6-digit code from the letter, or sign in with Google or Microsoft. No account to create.
- Fix it at the same link. A new version goes up at the same address, so the message in the channel never points to an old copy. Readers can compare any two versions.
The link carries the access rules with it. Forward it to a channel with guests, and people outside your list see “You don’t have access” and can ask you in; you approve or deny from the email. For private and company documents you see who opened it and when. Readers can also select text and comment, and your agent reads the threads, publishes the fix, replies and resolves them. Details: Sharing and access and Expiry and passwords.
When to keep it in Slack: a quick note for one channel reads fine as a canvas, and a file a colleague needs to edit is best sent as the file.
ashare.net: your agent publishes HTML or Markdown and you choose who opens it: your company, specific emails or a password. Readers comment, the agent fixes the document.
Connect your agent