Discord Inline Content Research — Final Findings

The CDN Webview Discovery

When you tap a file attachment on Discord mobile, it opens in an in-app webview pointing to a CDN URL like: https://cdn.discordapp.com/attachments/{channel}/{msg}/{filename}

Key insight: Discord determines content-type from the file extension, NOT the Content-Type header you send. So:

• .txt → text/plain; charset=utf-8 → shows as raw text
• .html → would normally be text/html → but Discord CDN forces download headers
• .md → opens in external app on iOS

The CDN sets Content-Disposition: attachment on non-image files, which forces download instead of inline rendering. This is a security measure — Discord doesn't want arbitrary HTML/JS running in their webview.

What's Actually Possible

1. Components V2 TextDisplay (BEST OPTION)

• Up to 4000 chars of markdown across all TextDisplay components
• Full Discord markdown (headers, bold, italic, lists, code, links, spoilers)
• Renders inline on mobile and desktop
• Can combine multiple TextDisplay + Separator + Container for structure
• No collapse/expand — content is always visible

2. Components V2 Container with spoiler: true

• Blurs content, tap to reveal (like image spoilers)
• NOT the same as collapsible — once revealed, stays revealed
• Good for hiding sensitive content, not for progressive disclosure

3. File Preview (Desktop Only)

• .txt files get inline code preview on desktop
• On mobile, opens in webview showing raw text
• No markdown rendering
• "Expand" button only on desktop

4. Image-based Content

• Convert markdown → image (PNG/SVG) → send as media
• Renders inline on all platforms
• Can't be selected/copied, not accessible
• Could use media gallery with spoiler for individual images

What Discord Explicitly Prevents

• No HTML rendering in file attachments (CDN forces download headers)
• No <details>/<summary> HTML elements in markdown
• No webview injection — CSP headers prevent script execution
• No iframe embeds — only specific embed types (link previews)

Recommended Approach for Justin

For long-form inline content:

Use Components V2 with multiple TextDisplay blocks + Container:

{
  "container": {"accentColor": "#5865F2"},
  "blocks": [
    {"type": "text", "text": "## Summary\nBrief overview here"},
    {"type": "separator", "spacing": "small", "divider": true},
    {"type": "text", "text": "### Details\nLonger content here..."},
    {"type": "actions", "buttons": [{"label": "Full Report", "style": "link", "url": "https://..."}]}
  ]
}

For collapsible content:

No native Discord solution exists. Best alternatives:

1. Spoiler container — blur/reveal (one-time)
2. Button → edit message — requires interaction handler (custom code)
3. Link to external page — host rendered HTML on CF Pages
4. Split across messages — summary message + threaded detail

For > 4000 chars:

1. Send .txt file alongside a V2 summary container
2. Host on CF Pages and link from the message
3. Split into multiple messages with V2 components