# Configuration Validation

The IDOL Server `ValidateConfig` action checks your configuration file for values that are missing or set incorrectly. It also provides information about deprecated parameters, and configuration changes that might affect your index. For example, it flags when:

- A parameter in your configuration has been deprecated. Where applicable, the server suggests an alternative configuration.

- A parameter in your configuration has an invalid value or type of value. Where applicable, the server returns information about the expected value or type.

- A parameter in your configuration file has not been read by the application, for example, because you have mistyped the name of a parameter.

- A parameter or configuration section is duplicated in your configuration. In this case, the validation also identifies the version of the configuration that is being used.
- A configuration section is present but does not contain any valid values.
- A configuration section is missing. For example, it reports when a field processing configuration references a property configuration section that does not exist.

- There are changes to the `[Properties]` configuration section when data has already been indexed. In this case, the warnings inform you whether you need to correct the configuration, re-index your data, or regenerate a subindex.

- There are changes to the languages configuration.

  NOTE: Language configuration warnings are persistent and continue even if you revert the configuration to its previous state, because some documents might have been indexed with the different settings. The warnings persist until you initialize your index.

The IDOL Admin user interface automatically flags any configuration validation errors, and you can use the interface to view the errors that the action returns.

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