The following are some of the important limits in the DynamoDB data model:

• There is an initial limit of 256 tables per region for an AWS account, but this can be changed by contacting AWS support.
• Names for tables and secondary indexes must be at least three characters long, but no more than 255 characters. Allowed characters are A-Z, a-z, 0-9, _ (underscore), - (hyphen), and . (dot).
• An attribute name must be at least one character long, but no greater than 64 KB long. Attribute names must be encoded using UTF-8, and the total size of each encoded name cannot exceed 255 bytes.
• The size of an item, including all the attribute names and attribute values, cannot exceed 400 KB.
• You can only create a maximum of five local secondary indexes and five global secondary indexes per table.

For a complete list of DynamoDB limits, refer to https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Limits.html.