Sentence Fragment Checker: What Actually Makes a Fragment

A complete sentence needs an independent clause — a subject and a verb that together express a full thought that could stand on its own. A fragment is punctuated like a sentence (capital letter, period at the end) but doesn't actually have that. "Because the lab was closed." looks like a sentence sitting there with its own period, but it isn't one — it's a dependent clause with nowhere to go, and the reader is left waiting for the rest of the thought.

This is why length is the wrong thing to check for. "Run." is a complete sentence — it has an implied subject (you) and a verb. "Walking to the lab early in the morning before most of the building was even awake." is a long string of words with no main verb doing anything, and no subject performing one — it's a fragment despite being far longer than "Run."

A dependent clause left standing alone: the group starts with a word like because, although, when, since, or if, sets up a condition or a cause, and then just stops without ever connecting to a main clause. "Although the results were inconclusive." needs something after it — "Although the results were inconclusive, the method itself held up" — or the subordinating word needs to be dropped so what's left can stand on its own.

A missing verb: the group has something that looks like a subject but no actual verb carrying out an action or state — often because a participle (ending in -ing or -ed) is doing the verb's job without the helping verb it needs. "The sample affected by contamination." has no real verb; "The sample was affected by contamination" fixes it by adding was.

A missing subject: the group opens with a preposition or a participial phrase that eats up the subject slot, leaving nothing to actually perform the verb. "By running the test twice, confirmed the result." has no subject for confirmed — someone or something has to be doing that confirming, as in "By running the test twice, we confirmed the result."

Fragments are easy to miss in your own writing for the opposite reason comma splices and run-ons are: they usually sound like a natural pause when you read them back in your head, especially short ones that follow a longer sentence for emphasis — a technique real writers use on purpose sometimes. The trouble is that in academic writing, an unintentional fragment reads as a mistake, not a stylistic choice, and it's hard to tell the two apart just by skimming your own draft.

StudyPilot's grammar checker flags fragments under its sentence-structure check, alongside run-ons and comma splices, with a one-click fix for each one rather than a generic "grammar error" label. It checks grammar, spelling, punctuation, and passive voice in the same pass, with no word limit on the free daily checks, so a full essay run through it catches this alongside everything else instead of you having to hunt for fragments on their own.