> ## Documentation Index
> Fetch the complete documentation index at: https://doc.lucidworks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Fallback

> Parser stage configuration specifications

export const schema = {
  "type": "object",
  "title": "Fallback",
  "description": "Handles documents that no other parser stage successfully processed, acting as a safety net by capturing raw content into `_raw_content_` for troubleshooting. Configure this as the last parser stage in the pipeline to catch all unhandled content types.",
  "required": ["type"],
  "properties": {
    "id": {
      "type": "string",
      "title": "Parser ID",
      "default": "34a16475-3cd4-476b-a8e3-137b31f877a9"
    },
    "label": {
      "type": "string",
      "title": "Label",
      "description": "Human-readable identifier displayed in the Fusion Admin UI, monitoring dashboards, and log messages. Use descriptive labels like `Parse Product PDFs` to aid debugging and team collaboration. Labels appear in performance metrics and error reports, making it easier to identify which stage failed.",
      "maxLength": 255
    },
    "enabled": {
      "type": "boolean",
      "title": "Enable this Parser Stage",
      "default": true,
      "description": "Controls whether this parser stage is active and available for use. When `false`, the stage is completely inactive regardless of other settings. When `true`, the stage runs according to its other configuration options."
    },
    "mediaTypes": {
      "type": "array",
      "title": "Media Types to match",
      "description": "Specifies the media types this parser stage handles. Documents with a matching media type are routed to this stage for parsing. See `inheritMediaTypes` to combine this list with the stage's built-in defaults.",
      "items": {
        "type": "string",
        "pattern": "^[^\\/]+\\/[^\\/]+$",
        "format": "rfc2646"
      }
    },
    "inheritMediaTypes": {
      "type": "boolean",
      "title": "Match default media types in this Parser Stage",
      "description": "Controls whether this stage combines its built-in default media types with those in `mediaTypes`. When `true`, both lists are merged. When `false`, only the `mediaTypes` list is used and must contain at least one entry. Set to `false` to override the default media types entirely.",
      "default": true
    },
    "ignoredMediaTypes": {
      "type": "array",
      "title": "Media Types to ignore",
      "description": "Specifies media types this parser stage excludes from processing. Documents matching an ignored media type are skipped even if they match `mediaTypes`. Use this to carve out exceptions from a broadly matched media type set.",
      "items": {
        "type": "string",
        "pattern": "^[^\\/]+\\/[^\\/]+$",
        "format": "rfc2646"
      }
    },
    "pathPatterns": {
      "type": "array",
      "title": "File names to parse",
      "description": "Restricts this parser stage to files whose names match the specified pattern. Use forward slashes (`/`) to join archive names with entry names when matching files inside archives. If no pattern is specified, the stage applies to all matching media types.",
      "items": {
        "type": "object",
        "properties": {
          "syntax": {
            "type": "string",
            "title": "Pattern type",
            "description": "glob uses bash shell-style wildcards and regex uses Java (PCRE-style) regex.",
            "enum": ["glob", "regex"],
            "default": "glob"
          },
          "pattern": {
            "type": "string",
            "title": "File name or pattern",
            "description": "glob examples are \"z.txt\" or \"*.md\" or \"/a/*/b/f.txt\". regex examples are \"z.txt$\" or \".*\\.txt$\" or \"^/a/[^\\/]*/b/f.txt$\"."
          }
        }
      }
    },
    "errorHandling": {
      "type": "string",
      "title": "Error Handling",
      "enum": ["ignore", "log", "fail", "mark"],
      "default": "mark"
    },
    "outputFieldPrefix": {
      "type": "string",
      "title": "Prefix parsed fields with",
      "description": "Sets a string prefix applied to all fields extracted by this parser, useful for namespacing or avoiding field name collisions. For example, `tika_` produces fields like `tika_title` and `tika_author`. Leave empty to apply no prefix.",
      "maxLength": 20,
      "pattern": "^$|^[A-Za-z_][A-Za-z0-9_\\-\\.]+$"
    },
    "metadataOnly": {
      "type": "boolean",
      "title": "Only parse metadata",
      "default": false
    },
    "maxBytesToKeep": {
      "type": "integer",
      "title": "Maximum bytes to keep",
      "default": 1048576,
      "description": "Sets the maximum bytes of raw content stored in the `_raw_content_` field. Content exceeding this limit is truncated to prevent memory issues and index bloat from large binary files. Set to `0` to store only document metadata without content."
    },
    "type": {
      "type": "string",
      "enum": ["fallback"],
      "default": "fallback"
    }
  },
  "additionalProperties": false,
  "category": "Other",
  "categoryPriority": 1,
  "unsafe": false
};

export const SchemaParamFields = ({schema}) => {
  const sanitize = str => {
    if (typeof str !== "string") return str;
    return str.replace(/^"(.*)"$/s, "$1").replace(/\\/g, "").replace(/"/g, "'");
  };
  const renderMd = str => {
    const s = sanitize(str);
    const text = (/[.!?]\)*$/).test(s) ? s : `${s}.`;
    return text.split(/(\*\*[^*]+\*\*|_[^_]+_|`[^`]+`)/g).map((part, i) => {
      if (part.startsWith("**")) return <strong key={i}>{part.slice(2, -2)}</strong>;
      if (part.startsWith("_")) return <em key={i}>{part.slice(1, -1)}</em>;
      if (part.startsWith("`")) return <code key={i}>{part.slice(1, -1)}</code>;
      return part;
    });
  };
  const {description, properties = {}, required: requiredProps = []} = schema;
  const visibleProps = useMemo(() => Object.entries(properties).filter(([, prop]) => !prop.hints?.includes("hidden")), [properties]);
  const renderProp = ([name, prop]) => {
    const isRequired = requiredProps.includes(name);
    const hasDefault = prop.default !== undefined;
    const rawDefault = prop.default;
    const hints = prop.hints || [];
    const isComplexDefault = hasDefault && (typeof rawDefault === "object" || typeof rawDefault === "string" && (rawDefault.length > 20 || rawDefault.includes('"')));
    const postBadges = [];
    if (prop.title) {
      postBadges.push(<><span className="text-stone-400 dark:text-stone-500">API property: </span>{name}</>);
    }
    const constraints = [];
    if (prop.minimum !== undefined && prop.maximum !== undefined) {
      constraints.push(`Range: ${prop.minimum} – ${prop.maximum}`);
    } else if (prop.minimum !== undefined) {
      constraints.push(`Min: ${prop.minimum}`);
    } else if (prop.maximum !== undefined) {
      constraints.push(`Max: ${prop.maximum}`);
    }
    if (prop.minLength !== undefined && prop.maxLength !== undefined) {
      constraints.push(`Length: ${prop.minLength} – ${prop.maxLength}`);
    } else if (prop.minLength !== undefined) {
      constraints.push(`Min length: ${prop.minLength}`);
    } else if (prop.maxLength !== undefined) {
      constraints.push(`Max length: ${prop.maxLength}`);
    }
    const fieldProps = {
      key: name,
      body: prop.title || name,
      type: prop.type,
      ...postBadges.length > 0 && ({
        post: postBadges
      }),
      ...isRequired && ({
        required: true
      }),
      ...!isComplexDefault && hasDefault ? {
        default: sanitize(String(rawDefault))
      } : {}
    };
    const isObject = prop.type === "object" && prop.properties;
    const isArrayOfObjects = prop.type === "array" && prop.items?.type === "object" && prop.items.properties;
    return <ParamField {...fieldProps}>
        {prop.description && <p>{renderMd(prop.description)}</p>}

        {prop.enum && <p>
            Allowed values: 
            {prop.enum.map((v, i) => <>{i > 0 && ", "}<code key={i}>{String(v)}</code></>)}
          </p>}

        {constraints.length > 0 && <p className="text-stone-500 dark:text-stone-400 text-sm">
            {constraints.join(" · ")}
          </p>}

        {isComplexDefault && <div className="flex">
            <p>
              <strong>Default:</strong>
            </p>
            <pre className="!my-0">
              <code>
                {JSON.stringify(rawDefault, null, 2)}
              </code>
            </pre>
          </div>}

        {isArrayOfObjects && <Expandable title="item properties">
            <SchemaParamFields schema={{
      properties: prop.items.properties,
      required: prop.items.required
    }} />
          </Expandable>}

        {isObject && <Expandable title="properties">
            <SchemaParamFields schema={{
      properties: prop.properties,
      required: prop.required
    }} />
          </Expandable>}
      </ParamField>;
  };
  return <div>
      {description && <p>{renderMd(description)}</p>}

      {visibleProps.map(renderProp)}
    </div>;
};

export const LwTemplate = ({title = "Key questions to get you started", icon = "sparkles", cta = "Powered by Agent Studio", linkHref = "https://lucidworks.com/demo/?utm_source=docs&utm_medium=referral&utm_campaign=docs_cta_ai"}) => {
  const [isLoaded, setIsLoaded] = useState(false);
  useEffect(() => {
    const timer = setTimeout(() => {
      setIsLoaded(true);
    }, 500);
    return () => clearTimeout(timer);
  }, []);
  return <div className="lw-template-container">
      <Card title={title} icon={icon}>
        {isLoaded && <span dangerouslySetInnerHTML={{
    __html: `<lw-template id="a029c1a9-28be-427e-b0e1-5d918920246a"></lw-template
            >`
  }} />}
        <Link href={linkHref} className="agent-studio-link text-left text-gray-600 gap-2 dark:text-gray-400 text-sm font-medium flex flex-row items-center hover:text-primary dark:hover:text-primary-light group-hover:text-primary group-hover:dark:text-primary-light">Powered by Lucidworks Agent Studio</Link>
      </Card>
    </div>;
};

[localhost link]: http://localhost:3000/docs/lucidworks-search/09-developer-documentation/config-specs/parsers/fallback-parser

[mintlify link]: https://doc.lucidworks.com/docs/lucidworks-search/09-developer-documentation/config-specs/parsers/fallback-parser

[old doc.lw link]: https://doc.lucidworks.com/managed-fusion/5.9/1uzufq

The Fallback parser stage is useful for processing data that Lucidworks Search does not have a specified parsing process for. Fallback does not technically parse data, since it does not know what to do with it, it simply copies the raw bytes into a Solr document. If your Lucidworks Search parser stage configuration encounters data it does not know how to parse, such as someone’s proprietary data file format, it will copy it as-is, whereas if it encounters recognizable data in more common file types, such as PDFs, Lucidworks Search will parse the text and metadata using Tika.

<LwTemplate />

The Fallback parser acts as the final stage that attempts to parse any documents that haven’t been parsed already. More commonly, the parser selects a stage specifically built to handle the data and runs that stage.

<Tip>
  When entering configuration values in the UI, use *unescaped* characters, such as `\t` for the tab character. When entering configuration values in the API, use *escaped* characters, such as `\\t` for the tab character.
</Tip>

<SchemaParamFields schema={schema} />