Is joking a sin? What does the Bible say about telling jokes?

Joking is an interesting topic and difficult to paint with one broad
brush. Biblically speaking, joking itself is not regarded as sin,
although in some instances, it certainly can be. Proverbs 18:21 tells
us that "the tongue has the power of life and death, and those who
love it will eat its fruit." James 3:3-12 compares the tongue to a bit
in a horse's mouth, a ship's rudder, and a fire. The tongue is a
powerful thing, and words can either bring great life or great hurt.
There are ways to joke that edify. "A cheerful heart is good medicine,
but a crushed spirit dries up the bones" (Proverbs 17:22). The Psalms
are full of references to laughter, which is what good joking
produces. But there is also a way to joke that is demeaning and
harmful, and we are called to "not let any unwholesome talk come out
of your mouths, but only what is helpful for building others up
according to their needs, that it may benefit those who listen"
(Ephesians 4:29).

Our words should always honor God and communicate that we value that
which He has made. The best way to know whether our joking is
bordering on the sinful is to seek the Holy Spirit and ask for His
conviction. He can make us sensitive to when a joke is appropriate and
when it may not be. If there is any doubt in our minds, or if our
consciences are being pricked by our joking, it is probably best to
forego it. There is also the issue of making others stumble, which we
can easily do with jokes that we may feel are perfectly innocent, but
which others see as offensive or hurtful. Our liberty should never be
exercised at the expense of another's conscience (Romans 14:13-17).

Occasional jokes and jesting, if they are appropriate, are probably
for the most part innocent. But there are those who make jokes so
often that they can hardly say a sentence without it containing a joke
of some sort. This is hardly the most appropriate lifestyle for a
Christian, however, as we are told to "live soberly, righteously, and
godly, in this present world" (Titus 2:12). As with all "gray areas"
in the Christian life, seeking God's wisdom regarding our speech is
the most profitable way to go (James 1:5).