what is the maximum length for meta_keyword, meta_description and meta_title

Question

While Uploading CSV,

There are some constraints that we have to follow, Like lengths of the attributes :

Please Provide the length of following attributes:

"meta_keyword"

"meta_title"

"meta_description"

Attribute Reference from : Magento Go - Knowledge Base

Answer 1

The limit is determined by the database limit for the attributes.

1. meta_title has the type varchar and is stored in the table catalog_product_entity_varchar. The limit on the value field of the table is 255.
2. meta_description and meta_keywords have the type text and is stored in the table catalog_product_entity_text. The limit on the value field of the table the limit of the text fields in mysql. For text is "L + 2 bytes, where L < 2¹⁶".

But the common sense says you shouldn't use large meta keywords and meta descriptions.
A meta description of 255 chars is more than enough.

As for meta keywords...you should ask a SEO expert on this, but I'm sure the recommended number does not go over 10.