Ocultar MCP Server

Ocultar

Ocultar is an open-source local PII/PHI masking engine for AI workflows.

It runs as a local HTTP sidecar. Send it text before it reaches a cloud LLM; it returns the same text with every piece of personal data replaced by a deterministic, reversible token ([EMAIL_9c8f7a1b], [PERSON_3a12b4cd], …). Originals are encrypted and stored in a local vault. Callers with the auditor token can restore them.

No PII ever reaches the upstream model.

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Quick start — Docker

export OCU_MASTER_KEY=$(openssl rand -hex 32)
export OCU_SALT=$(openssl rand -hex 16)
export OCU_AUDITOR_TOKEN=$(openssl rand -hex 24)

docker run --rm -p 4141:4141 \
  -e OCU_MASTER_KEY \
  -e OCU_SALT \
  -e OCU_AUDITOR_TOKEN \
  ghcr.io/ocultar-dev/ocultar:latest -serve 4141

Quick start — build from source

CGO_ENABLED=1 go build -o ocultar ./services/refinery/cmd/

OCU_MASTER_KEY=$(openssl rand -hex 32) \
OCU_SALT=$(openssl rand -hex 16) \
OCU_AUDITOR_TOKEN=$(openssl rand -hex 24) \
./ocultar -serve 4141

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API reference

GET /api/health

Returns engine status. No authentication required.

{
  "status": "healthy",
  "version": "1.14",
  "vault": { "status": "online" },
  "slm":   { "status": "online", "circuit": "closed" }
}

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POST /api/refine

Mask PII in text or JSON. No authentication required.

Request body: raw text string or any JSON value.

Response:

{
  "refined": "{\"message\":\"Hello [PERSON_3a12b4cd], your order [EMAIL_9c8f7a1b] is ready.\"}",
  "report": {
    "hits": 2,
    "types": ["PERSON", "EMAIL"]
  }
}

refined is a JSON-encoded string — parse it once to get the masked payload.

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POST /api/reveal

Restore vault tokens back to originals.

Authentication: Authorization: Bearer <OCU_AUDITOR_TOKEN> header required. Returns 403 if OCU_AUDITOR_TOKEN is not set on the server.

Request body:

{ "tokens": ["[PERSON_3a12b4cd]", "[EMAIL_9c8f7a1b]"] }

Response:

{
  "results": {
    "[PERSON_3a12b4cd]": "Alice Martin",
    "[EMAIL_9c8f7a1b]": "alice@example.com"
  }
}

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GET /api/entities · POST /api/entities · POST /api/entities/seed

Manage the persistent entity registry (pre-seed canonical names so all variants map to the same token). Requires Authorization: Bearer <OCU_AUDITOR_TOKEN>.

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Architecture

Ocultar runs two detection tiers before any text leaves the machine:

Tier 1 — Deterministic regex / heuristics (fast, zero-egress)

Tier 2 — SLM-based NER (higher recall, configurable endpoint)

Sends text to a local AI sidecar for named-entity recognition. The scanner is always initialized but produces no results unless a compatible sidecar is running at SLM_SIDECAR_URL. Point it at a privacy-filter or llama.cpp instance to activate NER.

SLM_SIDECAR_URL=http://localhost:8085 ./ocultar -serve 4141

Use SLM_ADAPTER=openai-chat for a llama.cpp / Qwen endpoint, or leave unset for the privacy-filter protocol (default).

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Privacy model

• Zero-egress design. Masked tokens ([EMAIL_9c8f7a1b], …) are the only data forwarded to the upstream model. Raw text is not transmitted.
• Local vault only. The mapping of each token back to its original value is stored in an encrypted DuckDB vault (vault.db) on the local filesystem using AES-256-GCM with HKDF-SHA256. The vault file is never transmitted.
• Raw prompt retention. The refinery logs each raw (unmasked) prompt locally to the vault to support the audit diff view. This data is encrypted at rest alongside the token mappings and is not sent anywhere. If prompt retention is not desired, do not configure OCU_AUDITOR_TOKEN — without an auditor token the reveal endpoint returns 403 and the diff view is inaccessible.
• Fail-closed design. If the refinery encounters an error or is unavailable, the gateway returns a 5xx error and stops — it does not forward raw text as a fallback.

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Configuration

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Building from source

Requires Go 1.24+ with CGO enabled (DuckDB and libphonenumber need a C compiler).

git clone https://github.com/ocultar-dev/ocultar.git
cd ocultar
make build

Run tests:

CGO_ENABLED=1 go test ./...

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License

Apache 2.0 — see LICENSE.