BerriAI/litellm · error · ValueError

pattern is required for regex patterns

Error message

pattern is required for regex patterns

What it means

ValueError raised in _add_pattern when a patterns[] entry declares pattern_type: "regex" but omits pattern. For regex patterns the `pattern` field is the regex source that gets re.compile()'d (case-insensitive); without it there is nothing to match.

Source

Thrown at litellm/proxy/guardrails/guardrail_hooks/litellm_content_filter/content_filter.py:744

    def _add_pattern(self, pattern_config: ContentFilterPattern) -> None:
        """
        Add a pattern to the compiled patterns list.

        Args:
            pattern_config: ContentFilterPattern configuration
        """
        try:
            extra_config: _PatternExtraLookup = {"keyword_pattern": None, "allow_word_numbers": False}
            if pattern_config.pattern_type == "prebuilt":
                if not pattern_config.pattern_name:
                    raise ValueError("pattern_name is required for prebuilt patterns")
                compiled = get_compiled_pattern(pattern_config.pattern_name)
                pattern_name = pattern_config.pattern_name
                extra_config = self._lookup_pattern_extra(pattern_name)
            elif pattern_config.pattern_type == "regex":
                if not pattern_config.pattern:
                    raise ValueError("pattern is required for regex patterns")
                compiled = re.compile(pattern_config.pattern, re.IGNORECASE)
                pattern_name = pattern_config.name or "custom_regex"
            else:
                raise ValueError(f"Unknown pattern_type: {pattern_config.pattern_type}")

            keyword_pattern: Final = extra_config["keyword_pattern"]
            keyword_regex: Final = re.compile(keyword_pattern, re.IGNORECASE) if keyword_pattern else None

            self.compiled_patterns.append(
                {
                    "regex": compiled,
                    "pattern_name": pattern_name,
                    "action": pattern_config.action,
                    "keyword_regex": keyword_regex,
                    "allow_word_numbers": extra_config["allow_word_numbers"],
                }
            )
            verbose_proxy_logger.debug("Added pattern: %s with action %s", pattern_name, pattern_config.action)

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Add the pattern field with the regex source, e.g. pattern: '\\d{3}-\\d{2}-\\d{4}'.
2. Verify the regex compiles case-insensitively (it is compiled with re.IGNORECASE) — test it locally with re.compile first.
3. Use name (optional) for a human-readable label; only pattern drives matching.
4. Quote YAML strings containing backslashes so the escape sequences survive parsing.

Example fix

# before
patterns:
  - pattern_type: regex
    name: internal-account
    action: BLOCK

# after
patterns:
  - pattern_type: regex
    name: internal-account
    pattern: 'ACCT-\\d{6}'
    action: BLOCK

# Lint pattern entries: regex requires a compilable pattern
import re

def lint_regex_patterns(patterns: list[dict]) -> list[str]:
    problems = []
    for p in patterns:
        if p.get("pattern_type") == "regex":
            pat = p.get("pattern")
            if not pat:
                problems.append(f"regex pattern missing 'pattern': {p}")
            else:
                try:
                    re.compile(pat, re.IGNORECASE)
                except re.error as e:
                    problems.append(f"invalid regex {pat!r}: {e}")
    return problems

def is_valid_regex_pattern(entry: dict) -> bool:
    """True when entry is a regex pattern with a non-empty, compilable source."""
    if entry.get("pattern_type") != "regex":
        return False
    pat = entry.get("pattern")
    if not isinstance(pat, str) or not pat:
        return False
    import re
    try:
        re.compile(pat, re.IGNORECASE)
        return True
    except re.error:
        return False

When it happens

Trigger: Config yaml contains litellm_params.patterns with an entry like {pattern_type: regex, action: MASK, name: my-rule} that lacks the pattern field.

Common situations: Example config copy-paste where the regex string was removed; author wrote the regex into `name` or `pattern_name` instead of `pattern`; YAML quoting issues silently dropped a multiline regex.

Related errors

• pattern_name is required for prebuilt patterns
• Content Filter: guardrail_name is required
• Unknown pattern_type: {pattern_config.pattern_type}
• Invalid format: file must contain 'blocked_words' key with l
• Error loading blocked words file {file_path}: {e}

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/1c4af7bc0e15e2ab. Report an issue: GitHub.