text field with custom content

in detail page, I need to view the result of some checks.

example:

• check if there are other customers who live in the same city
• check if there are other customers with the same name and surname
• etc

I would therefore have a line that reads: "check result: OK"

how can i do these checks? do I have to make a file with my function where I run the checks and do a return of the result? if so, where do I put the file?

I hope I have explained Thanks in advance for the help