Mastodon post preview
Free Mastodon Post Preview
A Mastodon post with a content warning is seen two ways: collapsed, showing only the warning text, and expanded. Most people only ever check the second one, which is the one fewer readers see first.
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Shows the collapsed and expanded views
Checks CamelCase hashtag formatting
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All about the Mastodon post preview
Content warnings create two versions of a post
When a Mastodon post carries a content warning, the body collapses behind the warning text and readers see only that line until they choose to expand it. Since the fediverse uses content warnings broadly, covering politics, food, long posts and eye contact rather than only distressing content, a large proportion of posts exist in two states. The collapsed view is the one that decides whether anyone reads the post, and it is the one people almost never check before publishing because their own composer shows the expanded version.
What to check before posting
Conventions here are firmer than on commercial platforms.
- The collapsed view, since that line is all most people will see initially.
- That the content warning describes the content accurately rather than teasing it, which is regarded as a misuse.
- That hashtags use CamelCase, so screen readers pronounce multi word tags correctly.
- That any image has alt text, which is expected rather than optional on Mastodon.
- The character count against your instance limit, which may be higher than the 500 default.
- Whether the post needs a content warning at all, since unnecessary ones dilute the mechanism.
Instance differences to be aware of
Mastodon is federated, so several things vary by server rather than being universal.
- Character limits are set per instance, so 500 is a default rather than a rule and yours may differ.
- Some instances have explicit policies about content warnings for particular subjects.
- Custom emoji sets are instance specific, so an emoji available on your server may not render elsewhere.
- Some servers defederate from others, meaning your post genuinely does not reach parts of the network.
- Local timeline visibility gives you an audience on your own instance that the preview cannot represent.
Who uses this tool
People learning conventions that are stricter than they expected.
- New arrivals unsure how a content warning will actually appear to readers.
- People who have been told their content warning read as clickbait.
- Anyone unsure whether their hashtags are formatted accessibly.
- Academics and researchers posting on subjects that often warrant warnings.
- Users on instances with non standard character limits.
Mastodon display reference
The defaults and the conventions.
| Element | Value | Notes |
|---|---|---|
| Post length | 500 characters by default | Instance configurable |
| Content warning | Collapses the post | Two views of one post |
| CamelCase tags | Expected | Screen reader accessibility |
| Alt text | Expected on images | Absence is noticed |
| Custom emoji | Instance specific | May not render elsewhere |
| Federation | Varies by instance | Some servers defederate |
| Discovery | Hashtags and boosts | No algorithm |
| Processing | In your browser | Nothing is uploaded |
Instances set their own limits and policies, so treat these as defaults rather than guarantees. Checked September 2026.
When this is not the right tool
A preview cannot tell you whether your post needs a content warning, since that depends on your instance rules and community norms rather than on the text. It also cannot represent your local timeline, which is a real part of who sees you and varies entirely by which server you joined. Since Mastodon has no algorithm, tagging matters far more than formatting, and the Mastodon hashtag generator is the more useful tool. For the post itself, use the Mastodon caption generator.
How teams picture using RepeatPost
“Honestly, the calendar is what sold me. I could see every channel in one view and spot the week we'd gone quiet. Before this I was juggling three spreadsheets and a Slack thread. Now I plan the month on a Monday morning and I'm done by half ten.”
Hannah Whitfield
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United KingdomJun 14, 2026“We run social for eleven clients and keeping them separate used to be a genuine anxiety of mine. Workspaces fixed that. Each client sits in their own space, approvals route to the right person, and I've stopped worrying that someone's going to push a dental practice promo to a restaurant account at 6am.”
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Chloe Baxter
Content Creator
AustraliaJul 11, 2026“I'm handling social for four small brands and writing captions was eating my whole morning. The AI drafts are actually quite usable now. I still rewrite maybe every third one to sound like the client, but starting from something beats staring at a blank box. The hashtag tool alone I'm using daily.”
Ananya Raghavan
Freelance Social Media Manager
IndiaJul 30, 2026“I sell fabrics and my customers find me on Instagram mostly. Posting used to be whenever I remembered, which was maybe twice a week. Now I sit down every Sunday evening, load up two weeks, and it goes out on its own. Sales have followed. I'd like to see WhatsApp added properly, that's my one ask.”
Chidinma Eze
Small Business Owner
NigeriaAug 18, 2026“Our team is five people and we were losing posts in Slack threads. Someone would approve something, someone else would tweak it, and nobody knew which version went live. The approval flow sorted that in a week. Fair play, it's the least glamorous feature on the site and it's the one I'd miss most.”
Niamh Gallagher
Social Media Lead
IrelandSep 02, 2026FAQs
Frequently Asked
Questions
The post body collapses behind the warning text, so readers see only that line until they choose to expand it. Your own composer shows the expanded version, which is why the collapsed view is so often unchecked.
More often than on other platforms. Across the fediverse they cover a wide range: politics, food, direct eye contact in photographs, even lengthy posts. Individual servers frequently set their own rules for specific subjects too.
No. The mechanism exists so people can decide whether to read something, and teasing behind it is regarded as a misuse. Describe the content accurately, and expect to be told if you treat it as clickbait.
Assistive software can then break a multi word tag back into its separate words. ClimateAction reads correctly where climateaction does not, and on Mastodon this is treated as an accessibility requirement rather than a style preference.
No, that is a default. Instance administrators can raise it, so your server may allow more. Because Mastodon is federated, several settings vary by server rather than applying across the whole network.
Far less than tagging does. Mastodon has no algorithm, so hashtags and boosts are the entire discovery system. A perfectly formatted untagged post still reaches only your existing followers.
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