When should you use custom match rules instead of automatic discovery?

Custom match rules earn their configuration cost specifically when automatic discovery's default behavior produces a Business Transaction list that's either too noisy, too coarse, or misaligned with how the business actually thinks about its own critical flows.

• High-cardinality URLs: paths like /orders/{id} generate a new BT per ID unless a rule normalizes them into one.
• Business-critical isolation: you need one specific flow, like checkout, tracked with its own dedicated health rule rather than lumped in with general traffic.
• Framework not fully auto-detected: a custom or in-house framework that automatic discovery doesn't recognize as a standard entry point.
• Parameter-based routing: the meaningful distinction between transaction types is in a request parameter or header, not the URL path itself.

The trade-off is maintenance: every custom rule is something a team has to keep aligned with the application as routes change, so it's worth reviewing the auto-discovered BT list first and only writing custom rules where discovery is demonstrably falling short, rather than replacing it wholesale from day one.