Selection-Scoped Formula Explainer

You have been handed a spreadsheet. Select a cell, and this says what that formula actually does — in the workbook's own words: the real column headers, the real defined names, the real values flowing through it right now, and what will break it.

Not “INDEX returns a value at a given position”. That is what the free web tools say, and it is useless. This says: D14 works out the delivered cost for BRK-220. It looks up the SKU in A14 in the Price list tab, takes the matching Unit price, multiplies by Qty in C14, then adds a fixed 8% carriage uplift that is typed into the formula rather than held in a cell — and it appears in 41 other formulas on this sheet.

Why the free explainers cannot do this

Paste-a-formula websites see Sheet2!$C$2:$C$500 as a piece of text. They cannot tell you it is the Unit price column, cannot show you what is in it, and cannot tell you the tab is called Price list — because they have never seen your workbook. You also have to copy the formula out of Excel to use them, and on an inherited model you have forty formulas to understand, not one.

The AI ones have the same blind spot and send your formula to their server, which is the end of the conversation in an accountancy practice holding a client's model.

Why not just use Copilot

Microsoft is retiring the in-cell COPILOT() function on 14 September 2026 and points everyone at the Copilot side pane instead. That pane is conversational, so the same question gets a different answer on different days; it does not reliably resolve references to header names; it will not tell you what is hardcoded or fragile; and it needs a paid Copilot seat.

This is the opposite of all four: instant, offline, and it never varies. The same formula always explains the same way, because the explanation is worked out by a parser and a set of templates rather than by a model. There is no API call, no key and no metering, which is why the free tier can be genuinely unlimited.

What the pane shows

• One sentence saying what the cell computes, in business terms.
• Step by step — the evaluation tree in reading order, innermost first, with the resolved names. Excel's Evaluate Formula with the syntax taken out and the names put in.
• What it reads — every cell, range and name the formula touches, with its label, its current value and the sheet it is on. Click any of them to jump there.
• Typed-in values — every literal in the formula, with a count of how many other formulas on the sheet contain the same one.
• Functions used — one plain line each, in context, not the Microsoft documentation.
• Watch out — volatile functions, whole-column references, cross-workbook links, an IFERROR swallowing real errors, a VLOOKUP doing an approximate match, and the cell in a filled column that does not match its neighbours.
• Copy it out as Markdown or plain text. Free, and always will be.

What it never does

It does not write to your workbook. It does not rewrite or “improve” your formulas, and where it notes that XLOOKUP would do in one call what your INDEX/MATCH does in two, that is information and nothing more.

The one exception is opt-in and off by default: showing the live value of each step means writing those steps to a hidden worksheet and deleting it again in the same operation, which clears Excel's redo history. Everything else works without it, and the pane says so rather than quietly turning it on.

What it costs

Free, permanently, unlimited: every layer above, on every cell, in every workbook, on every platform. No account. A single “explain a formula” is a commodity — five free websites do the naïve version — so charging for it would be charging for the part that is worth nothing.

£29 a year: the things a paste box structurally cannot do — every distinct formula on a sheet explained at once and deduplicated by pattern (a column of 400 identical formulas is one entry, not 400), the handover pack that comes out of it, the glossary of names and table columns, and the model summary. Prices and checkout.

Your data

Your formulas never leave this machine. There is no model, no server and no API call — the parser, the resolver and the templates are all inside the add-in. The only things that ever cross the network are a licence key and an anonymous install id, and only when you activate one. Privacy notice.

Known limits

• A reference into a workbook that is closed cannot be resolved. Excel is showing you its last cached value and there is no way to check it from a task pane, so the pane says exactly that rather than guessing at a label.
• Header inference is inference. It reads the nearest header row above the column. Where a sheet has no header row, or two stacked ones, the pane says what it found rather than inventing a name.
• Around sixty functions have a hand-written description, which covers the overwhelming majority of business formulas. Anything else is described by its shape and says so — it is never given a confident sentence nobody checked.
• Excel on Mac and on iPad are untested. The manifest permits them, so Microsoft lists them, but no verification run has happened on either.

Support

support@appgarden.co.uk. A formula this add-in could not read, or explained badly, is the most useful thing you can send — it goes straight into the test corpus.