From Team Fortress Wiki
- appid (uint32)
- The ID of the game to query assets from.
- language (Optional) (string)
- The ISO639-1 language code for the language all localized strings should be returned in. Not all strings have been translated to every language. If a language does not have a string, the English string will be returned instead. If this parameter is omitted the string token will be returned for the strings.
- currency (Optional) (string)
- The ISO 4217 code for currency specific filtering.
- true if the query was successful, false otherwise.
- A list of items with slot tags and prices in the chosen or all currency.
- An array containing the currency code and respective price, if a currency is specified only that currency value will be present. 
- original_prices (Optional)
- An array equivalent to prices in layout. Present when the item is on sale.
- A list of properties attached to the item 
- The name of the property.
- The value of the property.
- The "name" of the asset. This has no set content besides that it is an identifier that can be used in URLs such as those for Valve's store frontend.
- The class ID of the item.
- An array containing information related to the item's slot or special attributes. See tags
- An array containing friendly names for the tags attached to items.
- All prices are given as integers due to issues regarding precision. A double value can be obtained by dividing the price by 100.
- Note that for first party (Valve) games there may be a def_index property present, its value is a string that can be converted to an integer for use in schema item lookups.