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Minimal mime type implementation for use with the mail and rest-client gem.


Add this line to your application's Gemfile:

gem 'mini_mime'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mini_mime


require 'mini_mime'

# => "text/plain"

# => "text/plain"

# => "txt"

# => false


If you'd like to add your own mime types, try using custom database files:

MiniMime::Configuration.ext_db_path = "path_to_file_extension_db"
MiniMime::Configuration.content_type_db_path = "path_to_content_type_db"

Check out the default databases for proper formatting and structure hints.


MiniMime is optimised to minimize memory usage. It keeps a cache of 100 mime type lookups (and 100 misses). There are benchmarks in the bench directory

Memory stats for requiring mime/types/columnar
Total allocated: 8712144 bytes (98242 objects)
Total retained:  3372545 bytes (33599 objects)

Memory stats for requiring mini_mime
Total allocated: 42625 bytes (369 objects)
Total retained:  8992 bytes (72 objects)
Warming up --------------------------------------
cached content_type lookup MiniMime
                        85.109k i/100ms
content_type lookup MIME::Types
                        17.879k i/100ms
Calculating -------------------------------------
cached content_type lookup MiniMime
                          1.105M (± 4.1%) i/s -      5.532M in   5.014895s
content_type lookup MIME::Types
                        193.528k (± 7.1%) i/s -    965.466k in   5.013925s
Warming up --------------------------------------
uncached content_type lookup MiniMime
                         1.410k i/100ms
content_type lookup MIME::Types
                        18.012k i/100ms
Calculating -------------------------------------
uncached content_type lookup MiniMime
                         14.689k (± 4.2%) i/s -     73.320k in   5.000779s
content_type lookup MIME::Types
                        193.459k (± 6.9%) i/s -    972.648k in   5.050731s

As a general guideline, cached lookups are 6x faster than MIME::Types equivalent. Uncached lookups are 10x slower.

Note: It was run on macOS 10.14.2, and versions of Ruby and gems are below.

  • Ruby 2.6.0
  • mini_mime (1.0.1)
  • mime-types (3.2.2)
  • mime-types-data (3.2018.0812)


MiniMime uses the officially maintained list of mime types at mime-types-data repo to build the internal database.

To update the database run:

bundle exec rake rebuild_db

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.