Excel add-in that makes Excel formulas easy to understand, check, troubleshoot and fix.

Fd spy
Device frame

X-ray for Excel formulas

Instantly understand and troubleshoot complex Excel formulas


The horizontal view displays the result of each part of a formula in order to see how the result is calculated. You can also expand and collapse the formula parts by clicking the green result bar. 

The vertical view displays a formula as a tree of the parts of a formula. The parts can be expanded and collapsed.


Excel tells you when a formula has an error, but that’s it. Long formulas are even worse...where do you even start to track down the problem?

Now, FormulaSpy will pinpoint EXACTLY where the error is – no more guessing or wasting hours of your precious time.


Explore the cells that the formula uses, visit them and see their formulas, then drill into their references to gain a deep understanding of the entire calculation chain.

Modern formula editor

Live editor with instant feedback.


Format the formula at any time by clicking the 'Format'' button. This will auto-indent the formula to make it easier to read.


As you edit the formula, the border will turn green or red to indicate whether the formula is valid or not, making it very easy to check your formula for completeness.

Focus child (nested) formula

Click the 'Focus' button to syntax highlight only the formula that contains the cursor - color all other parts of the formula a light gray. This makes it easier to see which part of a fromula you're working on.

Find problems in your spreadsheet

Workbook Detective finds issues quickly. All errors, comments, external links, data connections and invalid data…all in one place…in a treeview that is easy to navigate.

Check compliance of styles and formatting

Style Explorer shows exactly what styles are being used (and abused) and where they are hiding.


The Style Map visually shows where a style is being used, so that you can easily look at the pattern to decide if anything is wrong or unexpected.


Styles are listed as well as all of their variations, where the style has been applied but the formatting has been altered slightly afterwards, so the cell is no longer using a ‘pure’ version of the style.


When you click on a style or one of its variants then Style Explorer will list the cells that are using it. Clicking on a style, or one the cells that are using it, will select the range in Excel.

Define allowed styles

Select cells that contain the styles you want, then find all instances other other styles - the ones you don't want. Alternatively, select some cells that contain styles that you want to find, then find all instances of these selected styles anywhere in your workbook.

Create custom functions (Lambda) from existing formulas

Lambda functions allow you to create new functions without VBA. Now, FormulaSpy enables you to create these new custom functions by using your existing formulas as templates.

Point and click

Convert an existing formula into a custom function by clicking on the parts that you want to convert into variables.

Rewrite existing formulas

Find and rewrite and rewrite and update formulas that can be enhanced to use the new custom function....with just a few clicks.

Check for issues in error-prone formulas

Some formulas are often used incorrectly or in a dangerous way. The Formula Checker will check your formulas for these types of issues.

VLOOKUP - Common issues

  1. Multiple data-types: Lookup function references a lookup range that has multiple data-types. All cells in the lookup range must have the same data type.
  2. 4th argument omitted (but data is sorted, so OK): 4th argument omitted, so non-exact match will be returned. The data is currently sorted so it's not required, but would be good to add for future robustness. Add 4th argument [FALSE], or ensure that the lookup range is sorted ascending.
  3. 4th argument omitted and data NOT sorted: 4th argument omitted, so non-exact match will be returned, therefore lookup range must be sorted ascending, but it's not. Add 4th argument [FALSE], or ensure that the lookup range is sorted ascending.
  4. Hard-coded column indexes: Hard-coded column indexes (adding new columns might cause your VLOOKUP formula to return incorrect results in the future). Rather use MATCH to find column index by name.
  5. Mismatched data-types: Lookup value to find (parameter 1) is a different data-type to the lookup range. Use CAST to cast the lookup value to the same type as the lookup range.
  6. Lookup value has spaces at start or end: Lookup value to find (parameter 1) has spaces at the start or end, which will affect matching and is probably not intended. Delete all leading and trailing spaces, unless it is intentional.

Download Example File 

System Requirements

 Excel 365, 2019, 2016, 2013 (Windows Desktop only)