This paper aims to reveal the rhetorical structure and the linguistic features of persuasive language in online advertisements of electronic products. Nowadays, the bulk of e-commerce is carried out in English, and it is often the case that non-native speakers are required to write different text types for various professional purposes, including promotional texts. This need has prompted the present study and the results have been used to build software to help native speakers of Spanish when writing promotional texts in English. The analysis reveals that these texts typically have two main rhetorical moves: one for identifying the product and another one for describing it. The latter move is further divided into two steps: one including objective features (size, weight, etc.) and the other focusing on persuading the potential customer. This is mainly achieved with the use of a relatively informal style (imperatives, contractions, clipping, subject/auxiliary omissions, etc.) and lexico-grammatical elements conveying positive evaluation (multiple modification, multal quantifying expressions, etc.). The findings show that online advertisements of electronic products may be regarded as a specific subgenre with particular macro- and microlinguistic characteristics, which have been identified in this paper for technical writing assistance.