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Response Redaction

AxonFlow can redact sensitive data from MCP connector responses before that data reaches your application or downstream model. This is one of the key controls that makes governed connector access useful in real production systems.

Concept page. This is the canonical explanation of how response-side redaction behaves. For where redaction sits in the full request/response flow, see MCP Policy Enforcement; for the PII detectors themselves, see PII Detection.

Why Response Redaction Exists​

Response-side enforcement matters because:

  • a connector can return sensitive data the caller did not explicitly expect
  • the returned data may contain PII, account numbers, national IDs, or regulated fields
  • once that data flows into an LLM or back to a user, the exposure has already happened

For RAG systems, enterprise copilots, support agents, and internal assistants, output controls are often as important as request-side blocking.

How It Works​

When a connector returns data, AxonFlow can:

  1. scan the response payload
  2. match configured policy patterns
  3. redact sensitive values
  4. return metadata showing that redaction happened

Example​

Original response:

{
  "customer_id": 12345,
  "name": "Jane Smith",
  "ssn": "123-45-6789",
  "credit_card": "4111-1111-1111-1111"
}

Redacted response:

{
  "customer_id": 12345,
  "name": "Jane Smith",
  "ssn": "[REDACTED:ssn]",
  "credit_card": "[REDACTED:credit_card]"
}

Depending on which response-processor and policy path is active, you may also see more generic placeholders such as [REDACTED]. The important contract is that sensitive values are masked before they continue downstream and that the response records which fields were changed.

Redacted responses stay valid JSON​

When the response payload is JSON, the redacted payload is always valid JSON. This matters because a downstream consumer — a Policy Enforcement Point, an MCP client, or the model itself — typically re-parses the redacted response and rejects malformed JSON.

Redaction is therefore structure-aware:

  • A PII value that sits in a string position is masked in place (it stays a string).
  • A PII value that sits in a numeric position — for example a national ID stored as an integer, {"nik": 3174012509900001} — is masked and coerced to a string ({"nik": "31**********0001"}), so the document remains valid JSON rather than producing an invalid token like 3174… with asterisks.
  • PII hidden behind JSON string escapes (for example a value encoded with \uXXXX) is decoded and matched, so escaping cannot smuggle a value past detection.

A JSON value that contains PII may be normalized (re-serialized) as part of this process; a payload with no PII is returned untouched. If redaction cannot produce a safe, valid result the response is failed closed (blocked) rather than forwarded — AxonFlow never emits a partially-redacted or structurally-broken response.

Response Metadata​

Redacted responses can include metadata such as:

{
  "redacted": true,
  "redacted_fields": [
    "rows[0].ssn",
    "rows[0].credit_card"
  ],
  "policy_info": {
    "redactions_applied": 2
  }
}

PII Categories Commonly Covered​

  • global identifiers such as credit cards, email addresses, and phone numbers
  • US-specific identifiers such as SSNs
  • India-specific identifiers such as Aadhaar and PAN
  • EU-related identifiers such as IBAN and other region-specific fields

The exact behavior depends on the policies active for the request.

What This Page Does Not Promise​

The current public docs should not promise configurable redaction modes such as full versus partial hashing, or special bypass permissions, unless those behaviors are explicitly documented and verified in the runtime you are deploying.

Treat response redaction as policy-driven output governance, not as a generic masking framework with every strategy available by default.

Configuration​

The PII_ACTION environment variable controls how detected PII is handled:

ValueBehavior
blockReject the response entirely
redact (default)Replace PII with [REDACTED:type] placeholders
warnAllow the response but log a warning
logAllow silently, record in audit trail

MCP connectors support a separate override via MCP_PII_ACTION. If set, it takes precedence over PII_ACTION for connector responses only.

SDK Handling​

Go​

resp, _ := client.MCPQuery(ctx, req)

if resp.Redacted {
    log.Printf("Redacted fields: %v", resp.RedactedFields)
}

TypeScript​

const resp = await client.mcpQuery(req);

if (resp.redacted) {
  console.warn('Redacted fields:', resp.redacted_fields);
}

Python​

resp = await client.mcp_query(...)

if resp.redacted:
    print(resp.redacted_fields)

Next Steps​

Connector Rollout Checklist​

Before exposing this connector to agents, make the governance boundary explicit:

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