Por la boca muere el pez is a fact-checking training guide. It explains the evolution of the journalistic practice, explores case studies and introduces tools that can be used to implement a verification project.

The guide includes information about financing verification projects.

The name of the guide is an idiom that literally translates to "Fish die through their mouths," with a meaning similar to that of the English idiom "Loose lips sink ships."

The tool is available in Spanish.