12 word secret phrase to private key conversion

This is the story, I created a new wallet on Trust Wallet for Ethereum, the generation of wallet private key is by the "12 word secret phrase", when I want to import the new wallet to Metamask because certain DApp supports metamask browser extension only.  Metamask can only import private key instead of 12 word secret phrase. 

Searched a bit on the Internet and found there is source code to convert the secret phrase to private key: 

https://github.com/iancoleman/bip39/releases

And there is an online version of the code available for the conversion of secret phrase to private key.

https://iancoleman.io/bip39/

And you can input the 12 secret phrase and convert to private key to be used in metamask.  But… wait a second, input the secret phrase over the Internet for processing?  Not a good idea. A rule of thumb is to be extemely careful when you trust something on the Internet.

So I downloaded the html code, and ran it internally in my own virtual web server which doesn't have Internet access at all, so there is no chance of leaking the information unless I am too careless?

And, tada.... it works, the private key were calculated and I successfully import the wallet to Metamask.

An interesting experience, and I learned some useless knowledge, again.

The article is not a good documentation and I haven't even been a documentation writer.