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Explore the expression language used throughout the Basis Theory API.
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Expressions provide a flexible templating language that can be used to apply custom transformations to token data.

Expressions can be used within many API endpoints, including:


The expression language used within the Basis Theory API is based on the Liquid template language. While all valid Liquid syntax is supported, Basis Theory expressions are typically formed from a combination of objects and filters.


Objects contain content that will be rendered when the expression is evaluated, and they are formed by wrapping a statement within double curly braces. For example, {{ data.card_number }} would be evaluated by rendering the card_number property within the data object.

The variables that are available for reference within an object expression depends on the context in which the expression is used. When including expressions during token creation (e.g., within search_indexes, fingerprint_expression or mask), the data variable is automatically bound to the token's data value. metadata is also available for expressions within fingerprint_expression.

When including expressions within Reactor or Proxy requests, token ids may be specified within object expressions, and each token id will be bound to the corresponding token's data value. See detokenization for further details about this process.