About the passive voice heuristic
Passive voice in English is typically formed with a conjugated form of the verb to be, such as am, is, are, was, were, be, being or been, followed by a past participle, as in "the report was written" rather than the active "she wrote the report." This tool looks for exactly that shape: a be-verb followed, within a short word window to allow for adverbs like "was quickly written," by something that looks like a past participle. Regular participles are easy to spot because they end in -ed, but English has roughly 150 to 200 common irregular verbs whose past participles don't follow that pattern, so this tool also checks against a built-in list of about 60 of the most frequently used irregular participles, covering words like written, done, made, seen, taken, given, broken, chosen, known, shown, spoken, driven, eaten, found, held, kept, left, lost, sent, sold, taught, told, thought, understood, won, brought, bought, caught, felt, heard, met, put, said, sat, stood and more. Because this is pattern matching rather than true parsing, it has known blind spots: it can flag a be-verb plus an adjective that merely looks like a participle, such as "the room was crowded," and it can miss a passive construction phrased in an unusual order. Treat every highlight as a prompt to look closer, not as an automatic error.
Not every match is wrong
Passive voice is the right choice when the actor is unknown, unimportant, or deliberately de-emphasized.
Edge cases exist
Adjectival past participles can trigger a false flag; use your judgment on each highlight.
A prompt, not a verdict
Use the highlights to review your writing, not as an automatic grammar correction.