Message Filter Object Structure

Overview

The messageFilter object configures server-side message filters. In v1.3.13, the supported filter type is messageFilter.pii.

messageFilter.pii rejects submitted message text that matches credential-shaped starter patterns or operator-defined regular expressions before the text reaches moderation, a model request, or message persistence.

Example

messageFilter:
  pii:
    starterPatterns:
      - sk_prefix
      - bearer_header
      - api_key_header
    customPatterns:
      - id: anthropic_api_key
        label: Anthropic API key
        regex: 'sk-ant-[A-Za-z0-9_-]{20,}'

Fields

messageFilter.pii

Key	Type	Description	Example
pii.starterPatterns	Array of Strings	Optional subset of built-in starter pattern ids to enable. Omit to enable all starter patterns.	starterPatterns: [sk_prefix, bearer_header]
pii.customPatterns	Array of Objects	Operator-defined patterns. Each entry requires `id`, `label`, and `regex`.

Built-in starter pattern ids:

sk_prefix: matches sk- style token prefixes.
bearer_header: matches bearer tokens in text.
api_key_header: matches api-key header-shaped text.

customPatterns

Key	Type	Description	Example
id	String	Stable pattern id used for logs and debugging.	id: anthropic_api_key
label	String	Human-readable label shown in the rejection message.	label: Anthropic API key
regex	String	JavaScript-flavor regular expression. LibreChat validates it at config load time and compiles it with the global flag.	regex: 'sk-ant-[A-Za-z0-9_-]{20,}'

Behavior

When submitted message text matches a configured PII pattern, LibreChat returns HTTP 400 with message_filter_pii_block and a message asking the caller to remove the matched credential type.

The filter checks:

Chat route user text submitted through the LibreChat UI.
Text content across all caller-supplied message roles in OpenAI-compatible Chat Completions requests.
Text content across all caller-supplied message roles in OpenAI-compatible Responses requests.

The filter evaluates text supplied in the request body. It does not scan file contents.