Updated Oct 2026
Platform limits and requirements
Each social platform sets its own limits on text and images. Each one also has rules for what a post needs. This page lists them for Twitter/X, LinkedIn, Instagram, Reddit, Facebook, and TikTok. Use it to see why a post is too long or can’t be approved. It also shows what a platform needs before you connect it.
Character limits
| Platform | Limit | Notes |
|---|---|---|
| Twitter / X | 280 characters | Every link counts as exactly 23 characters, however long it is. X Premium accounts get 25,000 characters. |
| 3,000 characters | ||
| 2,200 characters | ||
| 40,000 characters | ||
| 63,206 characters | ||
| TikTok | 2,200 characters | Over the limit? See Long TikTok captions can’t be approved. |
A post that’s over its platform’s limit can’t be approved. This goes for every platform. At the top of the post’s page, you’ll see “{N} characters over the {Platform} limit — Can’t be approved until it fits.” Under the editor, next to Approve, you see only the first part. Shorten the text, then approve.
The counter on a post’s page uses these limits. For Twitter/X, it counts each link as 23 characters as you type. So the number you see is what X will count. A post with a long link can show as under the limit even when the text looks long.
When you write a post yourself in the Create Post dialog, the text box stops at the lowest limit of the platforms you picked.
X Premium accounts
A standard X account gets 280 characters. If your X account has X Premium, you can post longer text. Tell PostSignOff once:
- Go to Settings → Connections.
- Under your connected X account, find X account tier.
- Pick X Premium (long posts).
Posts to that account can then be up to 25,000 characters.
Image limits
Each platform takes up to a set number of images per post.
| Platform | Max images per post |
|---|---|
| Twitter / X | 4 |
| 20 | |
| 10 | |
| 10 | |
| TikTok | 35 |
| 20 |
A post with more images than its platform allows can’t be approved. You’ll see “Media doesn’t meet {Platform}‘s rules”, with a note like this one: “X allows up to 4 image(s); this post has 6. Remove 2.” Remove images from that platform version until it fits. See Add images to a post for how the image tray works.
The Create Post dialog’s image tray holds up to 10 images. So in the dialog, Twitter/X is the only platform you can go over. Pick X and add more than 4, and a note appears: “{Platform} will use the first {N}.” Don’t rely on that note. The X version still can’t be approved until you cut it down to 4.
On a post’s page you can add more than 10 images. So the other limits matter there too.
Photos and videos in one post
- Instagram: several images become a carousel you can swipe through. It’s the only one that lets you mix photos and videos. You can post up to 10 items.
- Reddit: several images become a gallery post.
- Twitter/X, LinkedIn, Facebook: you get one post with several images in it.
- TikTok: several images become a photo post, not a video. TikTok can’t mix photos and a video in one post. Use up to 35 photos, or one video.
The other five take one video per post. They can’t take photos with it. A post that mixes them can’t be approved. You’ll see a note like “X can’t mix images and video in one post.”
What a post needs before it can publish
| Platform | Can it publish text-only? |
|---|---|
| Twitter / X | Yes |
| Yes | |
| Yes | |
| Yes | |
| No. Requires at least one image or video. | |
| TikTok | No. Requires at least one image or video. |
An Instagram or TikTok post with no media can’t be approved. On the post’s page, you’ll see “{Platform} needs at least one image or video” and “Can’t be approved without it.”
The Create Post dialog lets you pick Instagram or TikTok with an empty image tray. For Instagram, it shows a warning when you create the post:
“Instagram requires an image or video — its post can’t publish until you add one here or on the post’s page.”
TikTok gets no warning in the dialog. Add an image or video before you approve. You can add it in the dialog or later on the post’s page.
Connecting each platform
| Platform | What you need before you can connect it |
|---|---|
| You must be an admin of the Facebook Page you want to connect. While you connect, you pick the Page in a Choose a Page step. | |
| A business account linked to a Facebook Page. You connect that Page during the Facebook step. Instagram has no sign-in of its own here. If the linked business account can’t be found, you can still finish connecting. But posts to Instagram won’t publish until you reconnect with a Page that has one linked. | |
| You must be an admin of the organization you want to connect. While you connect, you pick it in a Choose an organization step. | |
| Twitter / X | No special account type is needed to connect X for posting. If you have X Premium, set the X account tier after you connect. |
| No special account type needed. See Reddit posts go to your own profile below. | |
| TikTok | No special account type needed. See Long TikTok captions can’t be approved and the PNG note below. |
See Connect your social accounts for the full connect and reconnect steps.
Platform quirks
Reddit posts go to your own profile, not a subreddit
PostSignOff has no setting to pick a subreddit. Your Reddit posts go to your own profile. They don’t go to a community.
Long TikTok captions can’t be approved
TikTok’s limit is 2,200 characters. A TikTok post that’s longer can’t be approved, same as any other platform. Shorten it until the counter is under the limit, then approve.
TikTok may reject PNG images
TikTok photo posts work best with JPEG or WebP images. TikTok may reject a PNG image when the post tries to publish, and the post shows as failed. If a TikTok post with images fails, look for PNG images. Swap them for JPEG or WebP, then retry. See Fix a post that didn’t publish.