Mester de juglaría is a Castilian-language literature

Spanish literature

Spanish literature generally refers to literature written in the Spanish language within the territory that presently constitutes the state of Spain...

 genre

Genre

Genre , Greek: genos, γένος) is the term for any category of literature or other forms of art or culture, e.g. music, and in general, any type of discourse, whether written or spoken, audial or visual, based on some set of stylistic criteria. Genres are formed by conventions that change over time...

 from the 12th and 13th centuries, transmitted orally

Oral tradition

Oral tradition and oral lore is cultural material and traditions transmitted orally from one generation to another. The messages or testimony are verbally transmitted in speech or song and may take the form, for example, of folktales, sayings, ballads, songs, or chants...

by "juglares" who made their living by telling and singing these stories in public places and palaces while performing short theatrical scenes, acrobatics or other amusements.

These anonymous stories were mostly cantar de gesta

Cantar de gesta

A cantar de gesta is the Spanish equivalent of the Old French medieval chanson de geste or "songs of heroic deeds".The most important cantares de gesta of Castile were:...

. Although versified to make
it easier to memorize, juglares probably often changed the story a little bit as they passed it to others.

There are more theories regarding the origin of these texts. The individualist theory states that these texts
were the creation of one poet and they didn't change much. On the other hand, the traditionalist theory
says that it is a collective work of the public and it was totally changed on its route.

Compared to the Mester de Clerecía

Mester de Clerecía

Mester de Clerecía is a Castilian literature genre that can be understood as an opposition and surpassing of Mester de Juglaría. It was cultivated in the 13th century by Spanish clergymen....

 the authors weren't educated, it treats popular topics, the language is simple and the metrics of the verses is irregular.

The most known examples of the works that can be classified as Mester de Juglaría is El Cantar de Mio Cid

Cantar de Mio Cid

El Cantar de Myo Çid , also known in English as The Lay of the Cid and The Poem of the Cid is the oldest preserved Spanish epic poem...

 and Representación de los Reyes Magos.