The Agency file contains information about the transit agency like contact information and a URL to the agency's fares webpage.

This file describes the different routes an agency operates. Each entry represents an individual route which includes different fields ranging from a description of the route to route and text colors which will show up on trip planning applications.

Calendar.txt contains the start and end dates for a schedule's service period. It also describes the service days that will run throughout a given service period (i.e. Monday - Friday, Monday - Thursday etc). Can be substituted for calendar_dates.txt and vice versa.

Trips.txt represents every trip operated by an agency. It is organized by route and service period. This file even has the option to denote wheelchair accessibility, if bikes are allowed, and blocks for interlined service.

Stop_times describes the actual arrival/departure times, stops used, and stop sequences per trip.

Stops.txt is an inventory of every stop an agency maintains. Each entry in the file represents an individual stop's information. This information includes latitude and longitude coordinates, the stop's name, and can include URLs or stop descriptions.

Calendar_dates describes the service exceptions an agency might run during a schedule. For example, suspending service for Christmas day or adding more service for Independence day could be represented in the GTFS. Can be substituted for calendar.txt and vice versa.

Shapes.txt contains the data used to describe a vehicle's path of travel along a route alignment.. This data includes the latitude and longitude coordinates for each point on the route alignment. Shapes.txt can also keep track of distance travelled along a route alignment.

Feed_info contains information about the GTFS feed. It can include fields that describe the default language and feed_start_date and feed_end_date for when a schedule has valid GTFS. Feed_info also contains information about the publisher of the GTFS which may be different from the transit agency.

Fare_attributes is one of four different files that are used to describe fares. Fare_attributes is responsible for displaying a fare's price, currency type, and payment method - important information for riders.

Fare_rules is used to establish which routes or origins and destinations a fare is valid on. For example, if a given route requires its own fare separate from the other routes.

Frequencies.txt might not be used in every GTFS feed, but it's a powerful file used to describe trips that repeat on regular headways.

This file is used to provide translations for any text field within the dataset. For example, it may be helpful for your GTFS to include multiple translations of a stop_name like "Grocery Parking Lot (west side)" since it does not refer to any named landmarks.