“How do topic tags work on Threads?”
How do topic tags work on Threads?
Short answer
A Threads topic tag lets people find your post by subject. You can add one topic per post, up to 50 characters, with or without a # sign. Spaces and special characters are allowed in the app. Tapping the tag opens search results for that topic, per the Threads Help Center (checked October 2026).
What a topic tag is
The Threads Help Center says that tagging a topic "allows others on Threads to discover your post and other posts associated with that topic in real time." When someone taps the topic in your post, Threads shows search results for posts related to it.
A topic tag is not exactly a hashtag. You can write it without a # sign, and it can have spaces in it, so "cat photos" works as one tag. Threads shows the tagged text in blue in the post.
Meta also publishes a page on why some topics can't be tagged. It says you may not be able to tag a topic if content associated with it consistently goes against the Terms of Use or Community Standards. Meta reviews these topics periodically and may allow them later if the content changes, and it asks people to report posts that go against its Community Standards.
The rules, in plain terms
These come straight from the Help Center article:
Note that the rules differ slightly depending on how the tag is created. The app limit is 50 characters with spaces and special characters allowed. The API topic_tag field has the same length range but blocks periods and ampersands.
- One topic per post. The article says you can include "up to one topic per post."
- Up to 50 characters long.
- Spaces and other special characters are allowed.
- The # sign is optional. If you start the topic with #, it is kept. The Help Center notes that including # may enable more functions on other platforms as Threads becomes interoperable with the fediverse.
- Some topics cannot be tagged, because posts about them repeatedly go against Meta's Terms of Use or Community Standards. Meta says it reviews those topics from time to time.
How to add one in the app
On threads.com from a computer, click the new post button, then click Tag or type # and enter a topic. You can pick one of the trending topics that appear, or type your own. Then click Post. The article lists the same steps for the mobile app.
If you type two topics, only one of them is the tag. Pick the one that best describes the post and leave the other as ordinary words.
Trending topics appear as suggestions while you type. Picking one is the fastest way to reuse a spelling that other people already use. If you type your own, the Help Center says the topic text shows in blue after you post, which is how you confirm it worked.
How the API treats tags
Scheduling tools publish through the Threads API, which has its own rules. Meta's docs say the preferred way is the topic_tag parameter. A tag set that way must be between 1 and 50 characters, and periods and ampersands are not allowed.
The docs keep an older route for backward compatibility: a tag typed inside the text. Only one tag is allowed per post, so "the first valid tag included in a post" is used. In-text tags have a stricter edge. A tag that starts with # ends before any space, tab, new line, period, ampersand, at sign, exclamation mark, question mark, comma, semicolon or colon. Whole numbers after a hash sign, like #1, are not turned into tags.
So "#cat photos" typed into the text of an API post tags only "cat". If you want a multi-word topic through a scheduler, use a tool that sends the topic_tag field. If a scheduler only has a text box, keep your tag to one word.
Choosing a tag
Because you get one, pick it like a headline label. A tag that names your subject ("indie hackers", "sourdough") is searchable, and Meta describes tagging as a way for others to discover your post and related posts in real time. A tag that is a joke or a slogan gives searchers nothing to find. Treat the tag as a discovery label.
On X, hashtags are a separate habit: they count as ordinary characters in a post, per X's character-counting docs. See the X character limit.
Because each post carries one topic, a week of posts is a week of small choices. A founder who writes about one product might rotate through three topics that match the three questions customers ask. Keep a list in your notes app so you do not invent a new spelling every time. "Indie hackers" and "indiehackers" are different topics, and a reader who taps one sees only that one's results.
If you use a scheduler, test one post first. Publish a draft with your tag, open it on Threads, and see whether the tag is blue and clickable. Then schedule the rest the same way.
If a tag you wanted is blocked, you can still write the word in the post. It just will not be a clickable topic. Do not try to disguise a blocked topic with odd spelling, since the point of a tag is that people searching the topic find your post.
Examples, app versus API
In the app, you type "indie hackers" in the Tag box. The topic is "indie hackers", with the space, and it shows in blue in your post.
Through the API with the topic_tag field, "indie hackers" is also fine: it is 13 characters, well under 50, and has no period or ampersand.
Through the API with a tag typed in the text, "#indie hackers" tags only "indie", because an in-text tag ends at the first space. Typing "#cats!" tags "cats", because an exclamation mark ends the tag. Typing "#1 tip" tags nothing, because a whole number after a hash sign is treated as a number sign, not a tag.
A tag with a period fails the topic_tag field. "Web3.0" is not allowed there, and "R&D" is not allowed either, because periods and ampersands are on the blocked list.
Where Threadgehog fits
Threadgehog writes posts and threads in your voice, and the draft you approve is the text your scheduler publishes. Add your one topic to the draft in the review queue, then use the API rules above to choose between the topic_tag field and a tag typed in the text. The X version Threadgehog writes carries no hashtags, so the topic tag stays a Threads habit.
Join the waitlist on pricing. To plan how many posts to write in the first place, see how often to post on Threads.
Questions
How many topic tags can I add to a Threads post?
One. The Help Center says up to one topic per post, and the API uses only the first valid tag.
How long can a Threads topic be?
Up to 50 characters, with spaces and special characters allowed in the app.
Do I need to type the # sign?
No. You can tag a topic without it, or start with # if you prefer.
Why did my API post only tag one word?
In-text tags end at the first space. Use the topic_tag parameter for multi-word topics.
Can I tag any topic?
No. Meta blocks topics where posts repeatedly break its Terms of Use or Community Standards.
Is a Threads topic the same as a hashtag?
Not quite. It is one label per post, can contain spaces, and opens topic search results.
Can a topic tag include a period?
In the app, special characters are allowed. Through the API, the topic_tag field does not allow periods or ampersands.
Do topic tags work with the fediverse?
Meta says including a # sign may enable extra functions on other platforms as Threads becomes interoperable with the fediverse.
Sources
- Threads Help Center: Tag a topic in your post (checked 2026-10-17)
- Threads Help Center: Why tagging certain topics isn't allowed (checked 2026-10-17)
- Meta: Threads API, create posts (checked 2026-10-17)
- X Developer docs: Counting characters (checked 2026-10-17)
- Threadgehog: home and FAQ (checked 2026-10-17)