Updated Jul 2026
Platform limits and requirements
Each social platform enforces its own character limit, image limit, and connection requirements. This page is a reference for all six. Use it to work out why a post is too long, why an image didn’t make it into a post, or what a platform needs before you can connect it.
Character limits
| Platform | Limit | Notes |
|---|---|---|
| Twitter / X | 280 characters | Every link in your post counts as exactly 23 characters, no matter how long the actual URL is. |
| 3,000 characters | ||
| 2,200 characters | ||
| 40,000 characters | ||
| 63,206 characters | ||
| TikTok | 2,200 characters | If your caption goes over, PostSignoff shortens it to fit when the post publishes. See TikTok cuts your caption short. |
The character counter under a post’s text box uses these limits and blocks you from submitting a post that’s over. For Twitter/X, the counter applies the 23-character link rule as you type, so the number you see already reflects what Twitter/X will actually count. A post with a long link may show as under the limit even though the visible text looks long.
Image limits
Each platform accepts up to a certain number of images per post. The Create Post dialog’s image tray holds up to 10 images total, but a platform with a lower limit than your tray only uses the first images, in the order you added them. The rest stay in the tray but aren’t sent to that platform’s post.
| Platform | Max images per post |
|---|---|
| Twitter / X | 4 |
| 20 | |
| 10 | |
| 10 | |
| TikTok | 35 |
| 20 |
Because the image tray caps at 10 images, Twitter/X is the only platform where this limit can actually be reached in practice. LinkedIn, TikTok, and Reddit’s limits are all higher than the tray ever holds. If a platform’s limit is lower than what’s in your tray, a note appears: “{Platform} will use the first {N}.” See Add images to a post for the full picture of how the tray works.
What each platform does with multiple images
- Instagram: multiple images become a swipeable carousel post.
- Reddit: multiple images become a gallery post.
- Twitter/X, LinkedIn, Facebook: multiple images attach to the one post as separate images.
- TikTok: multiple images become a photo post (not a video). TikTok treats a post as a photo post only when every attachment is an image. Mixing in a video switches it to a video 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. |
Instagram and TikTok both refuse to publish a post with no media attached. The Create Post dialog lets you select Instagram or TikTok with an empty image tray, but warns you at creation: “Instagram requires an image or video — its post can’t publish until you add one here or on the post’s page.” Add an image or video before the post is due to publish, either 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. During connect, you choose the Page in a Choose a Page step. | |
| A business account linked to a Facebook Page. You connect this Page during the Facebook step of the connect flow. Instagram doesn’t have its own separate sign-in. 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 a linked business account. | |
| You must be an admin of the organization you want to connect. During connect, you choose it in a Choose an organization step. | |
| Twitter / X | No special account type is required to connect X for posting. (Signing in to PostSignoff itself with an X account is separate: X can’t be used to create a new PostSignoff account, only to sign in to one that already exists.) |
| No special account type required. See Reddit posts go to your own profile below. | |
| TikTok | No special account type required. See TikTok cuts your caption short 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
When PostSignoff publishes to Reddit, the post always goes to your own Reddit profile. There’s no option to choose a subreddit. Every post is submitted as if you posted it yourself, not to any community.
TikTok cuts your caption short with no warning
If your post’s text is longer than TikTok’s 2,200-character limit, PostSignoff shortens it to fit when the post publishes. There’s no warning at approval time. The character counter in the dialog will show the post as over the limit, but nothing stops you from approving and publishing it. The caption is cut off at 2,200 characters when it goes out.
TikTok may reject PNG images
TikTok photo posts work best with JPEG or WebP images. A PNG image may be rejected by TikTok when the post tries to publish, showing as a failed post. If a TikTok post with images fails, try replacing PNG images with JPEG or WebP before retrying. See Fix a post that didn’t publish.