fehlerfrei
error-free
Without errors; completely correct and without defects.
Sie hat die Prüfung fehlerfrei bestanden.
She passed the exam without any errors.

error-free
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error-free
Without errors; completely correct and without defects.
Sie hat die Prüfung fehlerfrei bestanden.
She passed the exam without any errors.

The word is made up of 'Fehler' (error) and the suffix '-frei' (-free). The suffix '-frei' means 'without' and can be attached to many nouns to express that something is not present.
Ich suche ein Auto, das rostfrei ist.
I am looking for a car that is rust-free.
'Fehlerfrei' (error-free) can be used like an adverb to describe a verb. It then answers the question 'Wie?' (How?) and describes that an action is performed without errors.
Er spricht nach nur einem Jahr in Deutschland schon fast fehlerfrei.
After only one year in Germany, he already speaks almost without any errors.
The adjective is often used to describe the quality of texts, performances, or technical processes. Typical nouns are 'Text' (text), 'Diktat' (dictation), 'Aufsatz' (essay), 'Leistung' (performance), or 'Software' (software).
Bitte geben Sie einen fehlerfreien Text ab.
Please submit an error-free text.
sure / safe
'sicher' and 'fehlerfrei' can both have to do with correctness and functioning well. 'sicher' is more about something working reliably or being something you can depend on. 'fehlerfrei' is more precise and means that there really are no errors. A program can run reliably even if it has small bugs. A text is only 'fehlerfrei' if there are no errors in it. For exams, texts, or calculations, 'fehlerfrei' is often more precise.

Frau Demir gibt den Bericht erst ab, wenn er fehlerfrei ist.
Ms. Demir only submits the report when it is error-free.
Vor der Reise prüft sie, ob die Buchung sicher ist.
Before the trip, she checks whether the booking is secure.