It's a noun, and it's commonly used in various contexts.
Here are some examples:
* "Ang katapatan ay mahalaga sa isang relasyon." (Honesty is important in a relationship.)
* "Nakita ko ang katapatan sa kanyang mga mata." (I saw honesty in his eyes.)
* "Mahalaga ang katapatan sa paggawa ng negosyo." (Honesty is important in doing business.)