Why is it der Texteditor?

Texteditor is a compound noun, and German compounds take the article of their last word: der Editor. So it’s der Texteditor.

Sense 1
der

Meaning

[1] Computer program for editing texts

[1] Computerprogramm zum Editieren von Texten

Examples

[1] He wrote his letter with a text editor on the Computerä

[1] Er schrieb seinen Brief mit einem Texteditor am Computer.

Declension

1 Singular Plural
Nominativ der Texteditor die Texteditoren
Genitiv des Texteditors der Texteditoren
Dativ dem Texteditor den Texteditoren
Akkusativ den Texteditor die Texteditoren

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary