Formal:
* Functional: This emphasizes the object's ability to perform its intended purpose.
* Operational: This implies that the object is in working order and ready for use.
* Efficient: This suggests the object works well and without waste.
* Effective: This highlights the object's ability to achieve the desired outcome.
Informal:
* Working: This is the most common and straightforward option.
* Flawless: This emphasizes the absence of any issues or defects.
* Perfect: This suggests the object functions exceptionally well.
* As expected: This emphasizes that the object's performance meets expectations.
Other options:
* Sound: This implies the object is in good condition and reliable.
* Reliable: This suggests the object consistently performs as intended.
* In good working order: This is a more specific way to say the object is functioning properly.
The best word to use will depend on the specific situation and the desired emphasis.