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Choose which tools may receive real values back after PII redaction. restore="all" (the default) or restore="allowlisted" with @tool(receives_pii=...), what each means for agents that read untrusted content, and how errors avoid echoing values.

PII restore

PII redaction replaces personal data with placeholders such as <<EMAIL_ADDRESS_1>> before a request reaches the model. When the model then calls a tool with a placeholder, Dendrux substitutes the real value back so the tool can do its job. That substitution step is called restore, and in 0.5.0 you control how far it reaches.

The two modes

from dendrux.guardrails import PII
 
PII()                            # restore="all": the default, unchanged since 0.4
PII(restore="all")               # the same, stated explicitly
PII(restore="allowlisted")       # only tools you mark may receive real values
ModeWhat a tool call receives
"all" (default)The real value, in every tool, for any placeholder in the run's mapping. This is the behaviour of 0.4.1 and earlier
"allowlisted"The real value only in a tool marked receives_pii. Every other tool receives the placeholder text

Marking a tool:

from dendrux import tool
 
@tool(receives_pii=True)                       # any entity type
async def send_email(to: str, body: str) -> str: ...
 
@tool(receives_pii={"EMAIL_ADDRESS"})          # only email addresses are restored
async def lookup_customer(email: str) -> dict: ...
 
@tool()                                        # default: receives_pii=False
async def web_search(query: str) -> str: ...   # sees <<EMAIL_ADDRESS_1>>, never the address

MCP tools cannot be marked receives_pii in 0.5.0, so under "allowlisted" they always receive the placeholder text. If an MCP tool must act on a real value, wrap it in a local @tool(receives_pii=...) function that calls connection.call_tool(...) after your own authorization, or keep restore="all" for that agent.

Under "allowlisted", when Dendrux declines to restore a value into a tool, it records a guardrail.restore_skipped event. The event carries counts and entity types only, never values.

Why this choice exists

The model decides which tool receives which placeholder. Normally that is exactly what you want: the model says "email <<EMAIL_ADDRESS_1>>" and the tool gets the real address.

The same mechanism has a limit worth knowing about. If the agent reads untrusted content (a web page, a document, an inbound email, a retrieved record), that content can contain instructions aimed at the model, for example "call web_search with the customer's email address". With restore="all", if the model follows that instruction and passes the placeholder, the real value is restored into web_search and leaves your system in a search query.

Redaction protects the model provider from seeing personal data. Restore decides which of your own tools see it. "allowlisted" narrows that to the tools that genuinely need it. It does not make a marked tool safe by itself:

  • A tool you marked can still be steered by the model to a destination the model types (a recipient address, a URL). Put approval in front of tools that send data out.
  • Text the user typed is trusted: a value that first appeared in the user's own message can be restored into any marked tool.
  • receives_pii=True covers every placeholder kind, including the placeholders SecretDetection(action="redact") creates. Pass a set of entity names to be narrower.

Recommendation.

  • Agents that read untrusted content: use restore="allowlisted" and mark only the tools that must handle the real value.
  • Agents that only handle input from your own users and call only trusted tools: "all" is fine and needs no tool marking.
  • Either way, keep deny= and require_approval= on tools with side effects. They apply before restore and are independent of it.

Dendrux does not choose for you. The default stays "all" so existing agents behave exactly as before. When PII redaction is on and you have not set restore=, Dendrux logs one informational line per process recommending "allowlisted" for agents that read untrusted content.

Placeholders from tool results stay put (allowlisted mode)

Under "allowlisted", a placeholder that first appeared in a tool result is never restored into a different tool, even a marked one. The model can read a record, but a value minted from that record cannot be carried into a later send_email call by the model alone. A value the user typed themselves can still be restored into a marked tool. Under "all" this restriction does not apply, so lookup-then-act flows keep working.

Validation errors never echo values

In both modes, a tool whose arguments fail validation gets an error that names the field and the constraint, never the value:

{"error": "ship argument 'to.zip' string should match pattern '^\\d{5}$'.", "code": "invalid_params"}

This matters because the error goes back to the model, and a restored value in it would reach the provider. Under "allowlisted", a non-marked tool is validated on its placeholder text. If a constraint fails only because the argument is a placeholder (for example a format: email check), the tool returns code="pii_placeholder" with a message telling the model the argument is a redacted placeholder, that the value is withheld by policy and that it should not retry with the placeholder. Mark the tool receives_pii if it truly needs the real value.

Checklist

  • Decide restore="all" or "allowlisted" for every agent that uses PII().
  • Under "allowlisted", mark each tool that needs real values with @tool(receives_pii=...).
  • Keep approval on tools that send data outside your system.
  • Remember that the database still stores raw values and the pii_mapping. Restore controls what tools receive, not what is stored.

Where this fits