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20/08/2026 5:59 pm
TL;DR: Regex-based DLP struggles with business-specific sensitive data because pattern matches cannot distinguish true prescription numbers from lookalike purchase orders, according to Nightfall’s walkthrough of prompt-based entity detection. Context-aware detectors shift tuning work into natural-language definitions and examples, which makes precision and analyst efficiency the real governance test.
NHIMG editorial — based on content published by Nightfall: How to Build Custom Data Detectors Without Regex
By the numbers:
- The system confirmed readiness only after reaching 75% or higher accuracy on its classification check.
Questions worth separating out
Q: How should security teams detect custom sensitive data without relying on regex?
A: Use context-aware detectors that combine a natural-language definition, positive examples, and negative examples.
Q: Why do regex-based DLP rules create so many false positives?
A: Because regex can match structure, but it cannot interpret context.
Q: How do you know if a custom DLP detector is actually ready?
A: It is ready only when it has been tested against representative examples and clears a defined accuracy threshold before deployment.
Practitioner guidance
- Define detectors in business terms Describe the sensitive entity, its surrounding context, and the business workflow it belongs to before writing any matching logic.
- Add negative examples to every custom detector Include lookalike records that match the format but are not sensitive, so the detector learns what to ignore at the point of classification.
- Block production until accuracy is validated Use a minimum readiness threshold for each detector and require testing against both structured and unstructured sample files before rollout.
What's in the full article
Nightfall's full article covers the operational detail this post intentionally leaves for the source:
- Step-by-step detector construction flow for custom business identifiers
- Example positive and negative prompts used to reduce false positives
- Validation workflow for checking detector readiness before deployment
- Coverage details across PDF, text, Excel, and messaging channels
👉 Read Nightfall's walkthrough on prompt-based DLP detection for custom data →
Context-aware DLP for custom data types: are regex rules enough?
Explore further
20/08/2026 6:38 pm
Context-aware detection is becoming a control-plane issue, not just a content-classification feature. The real limitation in regex-based DLP is governance, because the control cannot express business meaning without continuous human tuning. Once organisations need to protect custom identifiers, AI-generated content, and lookalike records at scale, classification quality becomes part of identity and data governance. Practitioners should treat detector design as policy engineering, not as a one-off rule-writing task.
A question worth separating out:
Q: What should teams do when two business identifiers look the same?
A: Train the detector on the business difference, not just the syntax. Use negative examples, surrounding keywords, and workflow context to teach the system what to ignore. If the control still cannot separate them reliably, split the use cases and treat them as distinct policy objects rather than one shared pattern.
👉 Read our full editorial: Context-aware DLP is replacing regex for custom data detection
