> For a complete page index of the Captain API documentation, fetch https://docs.captain.dev/llms.txt?excludeSpec=true

# Custom PII Fields

* **Mask identifiers of your own**: with `mask_pii: true`, `pii_fields` takes up to 20 categories described in plain language with a tag you choose. Badge numbers, patient record numbers, bed assignments and the like are masked alongside the built-in categories, stored as `<YOUR_TAG>` and listed under that name in the masking report. See [PII Masking](/guides/pii-masking#custom-pii-fields).
* **Say whose values count**: `pii_instructions` takes plain-language guidance for the job (keep clinician names, mask patients and record numbers) and applies it to built-in and custom categories.
* **Two engines**: `captain-jev` is the default. Captain's classifier engine reads every token in context and decides which values are personal data and of which kind, your categories included. It catches dates of birth, member ids, usernames and plates, and leaves version, ticket and product names alone. The previous engine remains as `pii_engine: "captain-presidio"`. Details: [Engines and fallback](/guides/pii-masking#engines).
* **Fallback is explicit and reported**: when the `captain-jev` model is unreachable, `pii_fallback` chooses between masking with the legacy engine (default) and failing the file. Job status, [Get PII Report](/reference/jobs/pii/get) and every report object carry `engine` and `fallback`.