ANSWER

How do you find hidden business rules in a legacy system?

Reviewed October 16, 2026 · Reviewed by Paulo Pierrondi, founder.

Hidden business rules show up when you observe what the legacy system actually does, not what the manual says. Record real inputs and outputs over a full process cycle, read the code and logs where exceptions happen, and turn every behavior you find into a written rule with an owner, an example and a test criterion. A rule that is not written down does not enter the equivalence contract, and anything left outside the contract becomes a surprise at cutover.

Step by step

• Capture real inputs and outputs over a full process cycle, including month-end close and seasonal exceptions.
• Read the code, stored procedures and scheduled jobs looking for conditionals, parameter tables and hardcoded values.
• Interview the people who run the process and record manual adjustments, side spreadsheets and workarounds that became routine.
• Write each rule with an owner, a sample input, the expected output and evidence of where it was found.
• Validate the rules by running the replacement in parallel and treat each new variance as a possible unmapped rule.

How an agent does this

In AgenticosCore, discovery feeds the equivalence contract. The agent runs in shadow mode in Parallel, each variance becomes a candidate rule in Trail, and no new rule enters the contract without approval from one of your owners.