Better make sure it's a goodie.

Eye have a spelling chequer,
It came with my Pea Sea.
It plane lee marks four my revue
Miss Steaks I can knot sea.

Eye strike the quays and type a whirred
And weight four it two say
Weather eye am write oar wrong
It tells me straight a weigh.

Eye ran this poem threw it,
Your shore real glad two no.
Its vary polished in its weigh.
My chequer tolled me sew.

A chequer is a bless thing,
It freeze yew lodes of thyme.
It helps me right all stiles of righting,
And aides me when eye rime.

Each frays come posed up on my screen
Eye trussed too bee a joule.
The chequer pours o'er every word
Two cheque sum spelling rule.

The original version of this poem was written by Jerrold H. Zar in 1992. An unsophisticated spell checker will find little or no fault with this poem because it checks words in isolation. A more sophisticated spell checker will make use of a language model to consider the context in which a word occurs.
Most word or office programs are pretty good these days.