Firstly, trust is subjective, and you should always use your own judgement when downloading mods. However, there are some things you can do to help you find trustworthy mods.

1. Use a Source That Is Known to Be Trustworthy

The majority of authors publish their mods to Modrinth and CurseForge.

These websites check that the mods are what they say they are, and that they do not contain malicious code. You can also report malicious mods on those websites, and they will take action relatively quickly.

2. Check With Others!

If you are downloading a mod from a source that is not known to be trustworthy, you should check with others to see if they have downloaded the mod before from the location you're downloading from, and if they have had any issues with it.

If in doubt, you are welcome to ask in the Fabric Discord in the #player-support channel.

3. Avoid Common Malware Sites!

INFO

Malware sites may not be obvious to everyone. If you are unsure, you should ask for opinions from others or avoid the site altogether and rely only on trusted sources, such as Modrinth and CurseForge.

There are a lot of websites that claim to have mods for Minecraft, but are actually just malware sites. You should avoid these sites at all costs.

You can use antivirus software and websites like Windows Defender or VirusTotal to check the downloaded mods. However, do not rely entirely on those methods, because they can be sometimes incorrect.

Again, if in doubt, you are welcome to ask for opinions in the Fabric Discord in the #player-support channel.