Every German noun carries one of three genders, masculine, feminine, or neuter, and app courses generally teach this the same discouraging way: memorize "der," "die," or "das" alongside each individual word, since German gender mostly can't be predicted from meaning the way it sometimes can in Spanish or French. That's true for meaning. It's substantially less true for form. A meaningful share of German nouns signal their own gender through their ending, a pattern real enough to guess by, and one most courses never present as its own standalone rule.
The endings worth actually memorizing
Nouns ending in -ung, -heit, -keit, -schaft, or -ion are reliably feminine, with almost no exceptions: die Zeitung (newspaper), die Freiheit (freedom), die Möglichkeit (possibility), die Gesellschaft (society), die Nation. This single cluster of suffixes covers an enormous share of abstract nouns that show up constantly in news writing, political and social coverage especially.
Nouns ending in -chen or -lein are always neuter, regardless of what the underlying word's own gender would otherwise be: das Mädchen (girl) is neuter even though a girl is obviously female, because -chen is a diminutive suffix that overrides the base word's gender entirely. This is a genuinely useful shortcut precisely because it's absolute, no exceptions to hedge against.
Nouns ending in -ismus, -or, or -ling tend masculine: der Journalismus, der Motor, der Frühling (spring). This pattern is less airtight than -chen or -ung, but reliable enough to guess with reasonable confidence on an unfamiliar word before confirming it.
Why apps rarely teach this as its own rule
Vocabulary-drill apps introduce nouns one at a time, each with its article memorized as a fixed pair, which is a reasonable way to build a working vocabulary but obscures the pattern sitting underneath the individual words: the suffixes themselves are doing predictable work, but a course that never separates the suffix rule from the vocabulary item leaves a learner treating every new noun as an unrelated fact to memorize from scratch, rather than a case that a general rule usually already predicts.
A worked example, applying the rule live
Take an unfamiliar noun in a real sentence: "Die Verhandlung dauerte drei Stunden" (the negotiation lasted three hours). Even without knowing "Verhandlung" specifically, the -ung ending predicts feminine before you've looked anything up, and the sentence's own article, "die," confirms it. Compare "Der Vorschlag wurde abgelehnt" (the proposal was rejected): "Vorschlag" doesn't carry one of the reliable suffixes above, so no shortcut applies, and the article "der" in front of it is doing the only work of telling you the gender, the ordinary way. Knowing which nouns the shortcut covers, and which ones it simply doesn't apply to, is as much the skill as the suffix list itself.
Where the pattern stops being reliable, and why that's fine
These suffix rules cover a real, useful minority of German vocabulary, not the majority, and plenty of common nouns, der Tisch (table), das Auto (car), die Blume (flower), carry no predictive ending at all. The rule isn't meant to replace learning gender the ordinary way, it's meant to remove the guesswork specifically on the subset of vocabulary where German's own morphology already tells you the answer, freeing up the deliberate memorization effort for the words that genuinely need it.
Foreign-borrowed nouns follow their own separate pattern
Words borrowed into German from English or French often default to neuter regardless of what suffix rule might otherwise apply, especially recent tech and business borrowings: das Update, das Meeting, das Interview. This is worth knowing as its own small category rather than trying to force a borrowed word into the -ismus or -or pattern above, since a word like "der Computer" (masculine, following the -er agent-noun pattern common to native German nouns) sits right alongside "das Handy" (cell phone, neuter, a borrowed-feeling coinage with no predictable native suffix at all), and treating every foreign-looking noun as automatically neuter would get "der Computer" wrong just as often as guessing blind would.
The payoff, before you've even reached the verb
Recognizing a reliable-gender suffix on an unfamiliar noun mid-sentence lets you predict its article, and therefore its grammatical role in the sentence, before you've fully parsed what the word even means, which matters because German's case-marking system (covered separately in Why German Case Endings Matter More Than You Think) depends on knowing a noun's gender to correctly read which case ending is attached to it. A learner who can predict gender from form alone effectively gets a small head start on parsing an unfamiliar sentence, rather than needing to already know the word to know how the rest of the sentence relates to it.