Tequila can only be made within particular regions of certain Mexican states; including 124 municipalities of Jalisco (including the town of Tequila and the majority of modern tequila production), 8 municipalities in Nayarit, 7 municipalities in Guanajuato, 30 municipalities in Michoacan, and 11 municipalities in Tamaulipas.
The CRT requires the following to be on all tequila labels:
Type - (tipo) or category of tequila (blanco, añejo, reposado, etc.)
Purity - (only 100% agave is labelled as such and if it doesn't say it is 100% agave on the label then it is a mixto). *Note that since the shortage in 1999-2000, several companies have changed their 100% agave products into mixto to keep prices low. Terms like “100% natural,” “100% Mexican,” “100% natural product,” “100% aged” or other similar statements are prohibited
NOM - (distiller registration number). Take a NOM list with you. The brand (name) is not any real indication of who makes the product, so a good NOM list is an absolute necessity to know who the players areDistiller's name and address (not always shown in full on the front and sometimes only indicating a town and state). This may be the parent company's or corporation's address, or the administration office
CRT - indication the Tequila Regulatory Council has certified the product - not a guarantee of quality, however - simply that the CRT has approved the process at the company's site and it meets the legal requirements
Hecho en Mexico - Made in Mexico. All 100% agave tequilas can only be made and bottled in Mexico. It can also say "producto de Mexico" or "elaborado en Mexico." Hecho a mano means 'handmade' and is not an official term but usually indicates traditional or artesanal production processes
DOT - denomination of origin (tequila) number, indicating compliance with Mexican regulations regarding where the product was made. This is not on all labels
Brand name - Usually accompanied by a graphic or a logo and a trademark identifier such as ® or “MR” ™.
Alcohol content - Tequilas in Mexico are usually 38-40% alcohol, but legally may be higher, up to 50%;
Any additives - such as flavor or aroma
The volume of the contents in milliliters (i.e. 200, 375, 500 or 750 ml) or litres
Lot or batch: each bottle must be engraved or stamped with the coded identification of the lot to which it belongs (see image, below)
Any warning statements set forth in health legislation or any information required by other legal provisions applicable to alcoholic beverages
Of course it should also say "tequila" on the label - otherwise it could be anything inside the bottle. But the word 'tequila' alone without 100% agave also means it is a mixto.
Some bottles may have a number to indicate the batch size and the bottle's number in that batch. This is not a requirement, but it may also indicate the size of any particular production.
Silver/Blanco/Joven: generally unaged (or very briefly aged, for smoothness, e.g. “Suave” styles); full of agave flavor, but also heat, and an impression—but not taste—of vegetal sweetness
Gold: Basically a hybrid type, usually a mixto with coloring added to make it seem aged when it’s not; best bet is buying a brand that actually states “100% agave” on the label
Reposado: Meaning “rested,” aged in wood barrels for 2 months to under a year
Anejo: Aged between 1 and 3 years, the widest available complexly aged tequila, with softened heat and good wood character; too much aging isn’t recommended, as tequila is about expression of vegetal agave
Extra Añejo: A newer category, aged over 3 years, greater wood notes from time in barrel, deeper color, complex layers of sweet and spice
Cristalino: An Extra Añejo that goes through an additional filtration to remove the amber color, resulting in a clear tequila that has been aged (not to be confused with a blanco)