Check a mod yourself
Open any Minecraft mod jar and read what is inside it. You do not need an account, and the mod does not need to be certified by us.
Open a jar
What you will see
The jar is unpacked and every file inside it is listed. For each compiled class we show what it declares, the methods it defines, every external call it makes, and the text baked into it. Configs, manifests and language files are shown as written. Textures are shown as images.
That covers the question most people are actually asking. A mod that starts operating system processes, or reaches into your browser profile, or has a webhook address baked into it, will show that here.
What it is not
This shows structure, calls and text. It does not reconstruct Java source. Read what you find as evidence to weigh up: a clean-looking archive still guarantees nothing, and an unfamiliar call on its own proves nothing either.
This is separate from certification
Reading a file here does not certify it and does not create a record. If you want the artifact reviewed reviewed and issued a certificate, that is the certification process and it starts with a publisher account.
Only upload what you are allowed to
Open files you have obtained legitimately. Mod authors hold copyright in their work, and this tool exists so you can inspect what you are about to run, not to redistribute anyone's code.
If you find something
If a mod is doing something it should not, and it carries one of our badges, tell us. If it does not carry a badge, report it to the platform hosting it. Either way, do not install it.