This paper presents AttentionApp, an interactive demonstration system designed to support the inspection and linguistic analysis of attention mechanisms in Transformer-based language models for Portuguese. The tool allows users to input sentences in Portuguese and visualize attention distributions across layers and heads, enabling fine-grained qualitative analysis of syntactic and semantic patterns captured by the model. AttentionApp is intended as a research-oriented tool, facilitating exploratory analysis, hypothesis generation, and interpretability studies for Portuguese Natural Language Processing.