Note: Excel has several built-in data validation rules for numbers. This page explains how to create a your own validation rule based on a custom formula.
To allow only numbers in a cell, you can use data validation...

To count cells that do not contain many different strings, you can use a rather complex formula based on the MMULT function. In the example shown, the formula in F5 is:
{=SUM(1-(MMULT(--(ISNUMBER(SEARCH(TRANSPOSE(...

Note: Excel contains many built-in "presets" for highlighting values with conditional formatting, including a preset to highlight cells that contain specific text. However, if you want more flexibility, you can use your...

To extract all matches based on a partial match, you can use use an array formula based on the INDEX and AGGREGATE functions, with support from ISNUMBER and SEARCH. In the example shown, the formula in G5 is:
=IF(F5...

To get the position of the first match that does not contain a specific value, you can use an array formula based on the MATCH, SEARCH, and ISNUMBER functions. In the example shown, the formula in E5 is:
{=MATCH(FALSE...

To count the number of specific words or keywords that appear in a given cell, you can use a formula based on the SEARCH, ISNUMBER, and SUMPRODUCT functions. In the example shown, the formula in C5 is:
=SUMPRODUCT(--...

To lookup the latest file version in a list, you can use a formula based on the LOOKUP function together with the ISNUMBER and FIND functions. In the example shown, the formula in cell G7 is:
=LOOKUP(2,1/(ISNUMBER(...

To categorize text using keywords with a "contains" match, you can use the SEARCH function, with help from INDEX and MATCH. In the example shown, the formula in C5 is:
{=INDEX(categories,MATCH(TRUE,ISNUMBER(SEARCH(...

To filter data to include data based on a "contains specific text" logic, you can use the FILTER function with help from the ISNUMBER function and SEARCH function. In the example shown, the formula in F5 is:
=FILTER(...

To use XLOOKUP to match values that contain specific text, you can use wildcards and concatenation. In the example shown, the formula in F5 is:
=XLOOKUP("*"&E5&"*",code,quantity,"no...

To sum if cells contain either one text string or another (i.e. contain "cat" or "rat") you can use the SUMPRODUCT function.
Background
When you sum cells with "OR" criteria, you need to be careful not to double count...

To test a range for numbers, you can use a formula based on the ISNUMBER and SUMPRODUCT functions. In the example shown, the formula in G5 is:
=SUMPRODUCT(--ISNUMBER(C5:C9))>0
How this formula works
Working from...

To test a cell for one of many strings, while excluding others, you can use a formula based on the SEARCH, ISNUMBER, and SUMPRODUCT functions. In the example shown the formula in C5 is:
=(SUMPRODUCT(--ISNUMBER(SEARCH(...

If you want to test a cell to see if it contains all items in a list, you can do so with a formula that uses the SEARCH function, with help from the ISNUMBER, SUMPRODUCT, and COUNTA functions.
Context
Let's say you...

To test if one of several values exists in a range of cells, you can use a formula based on the SUMPRODUCT function. In the example shown, the formula in cell D5 is:
=SUMPRODUCT(--(rng=B5:D5))>0
where "rng" is the...