Stack effect checking failure conditions are reported in one of two ways:

•	Stack effect tools report them when fed quotations interactively
•	The Optimizing compiler reports them while compiling words, via the Batch error reporting mechanism

Errors thrown when insufficient information is available to calculate the stack effect of a call to a combinator or macro (see Combinator stack effects):

do-not-compile ( word -- * )

unknown-macro-input ( macro -- * )

bad-macro-input ( macro -- * )

Error thrown when a word's stack effect declaration does not match the composition of the stack effects of its factors:

effect-error ( inferred declared -- * )

Error thrown when branches have incompatible stack effects (see Branch stack effects):

unbalanced-branches-error ( word quots declareds actuals -- * )

Inference errors for inline recursive words (see Recursive combinator stack effects):

undeclared-recursion-error ( word -- * )

diverging-recursion-error ( word -- * )

unbalanced-recursion-error ( word height -- * )

inconsistent-recursive-call-error ( word -- * )

More obscure errors that are unlikely to arise in ordinary code:

recursive-quotation-error ( quot -- * )

too-many->r ( -- * )

too-many-r> ( -- * )

missing-effect ( word -- * )