What words are restricted in Roblox's text chat?

There isn't a comprehensive list on roblox's filter, as it's run by an AI being slowly taught by millions of users. The best way to find out what you can and can't say is via trial and error, unfortunately. You can expect to be able to type things with more expression and slightly stronger language, but the platform remains family-friendly.

Basically, type a bunch of stuff in a free private server, and see whether it "tags" (gets filtered) or not.

A comprehensive list of words and phrases is impossible to provide, given how the filter works today. However, the wiki only explicitly defines two age groups:

• Less than 13.
• 13 and older.

There are words and phrases that are censored in both, with no explicitly stated age cap on when they stop being censored. So long as you play Roblox, you're likely to encounter the filter.

? How it Works

According to the wiki, the filter of the modern age is provided by the CommunitySift service which applies multiple rules and text classification techniques to filter phrases. As @Corsaka pointed out in their answer, the service is a controlled neural network which constantly studies what users say. This enables it to learn and evolve with language:

The system is a controlled neural network, which is constantly studying what users say so it can learn and evolve with the language as new bypasses and idioms are created.

? False Positives

The filter gets criticism for producing false positives with words such as:

"can't", "hi", "ok", "secret", "the", "we", "my", "well" "um", "town", "bucket" and "some"

These words sometimes get censored, and according to Roblox staff and common users, it happens quite frequently; however, it is noted that the frequency of censorship has reduced in recent years.

? Numbers

Numbers are partially censored, though the details on what criteria the system uses for them are non-existent. The reason for the censorship of numbers is primarily focused on preventing personally identifiable information (such as age, addresses and phone numbers) from being revealed:

...namely, to avoid underage users sending messages with personally identifiable information such as age, addresses and telephone numbers.

In February of 2021, this feature has been slightly removed which enables < 13 accounts to say numbers, but only to a certain extent (which is not given).

? LGBTQ+

It's worth noting that the filter previously had a hard line on words such as:

"gay", "homosexual", "lesbian", "bisexual" and "transgender"

These words were filtered for being sexual terms and Roblox heavily frowns upon anything related to sexual content. However, this hard line has since been adjusted to focus on negative connotations in an effort to support Roblox's LGBTQ+ user base who may identify as any of the aforementioned terms or the alike.

? Can't

Oddly enough, the word "can't" has been consistently been filtered with no apparent reason. However, the current concept as to why this occurs is that the filter may think the word is a swear word used in the UK.

? A Little History Gem

Once upon a time, this would've been a completely feasible request as Roblox previously used a blacklist that came with the Roblox Player and was stored in a file named diogenes.fnt.