Optimisation for Google Sheets
Plumline works out the best allocation your spreadsheet allows — how much to make, buy, ship or staff — then proves it against your own formulas instead of asking you to trust it.
A worked example · drag to change the limits
runs in your browser — the real add-on runs in your sheet
Nothing to set up
Open the panel and the problem is already there. Plumline works out which cells are the quantities to decide, which total is the goal, and which limits apply — and it names them with the labels you wrote, not with cell addresses. If it reads something wrong, you correct it. You never build the model from scratch, and you never see “no model defined”.
The part that matters
A solver is one of the few tools whose output you cannot check by looking at it — you asked precisely because you did not know the answer. So Plumline does not ask for trust. It writes the solution back, lets Sheets recalculate on its own, and shows you that both numbers agree. Every limit is listed with how much you used and how much is left, so you can see which one is actually holding you back.
When it can't
The real complaint about the solvers in this category is not that they fail. It is that they fail without saying why — or worse, work one day and quietly stop respecting a limit the next — and you lose an afternoon doubting your own spreadsheet. When a model can't be solved, Plumline names the cell and the reason in plain terms, every time, the same way.
Whole numbers when you need them
Tick whole units only and Plumline searches for the best integer combination instead of rounding a fractional answer — which is not the same thing, and is usually worse. Try it on the example above: set the hours to 30. The fractional best makes 1.67 of product C; the whole-number best rebuilds the mix entirely rather than rounding that 1.67. If the search runs out of time holding a valid answer, Plumline tells you it is the best it found, not the best there is.
Why it's different
These aren't strawmen. They're the failures that fill the reviews of the solvers already in the store.
“It told me non-linear for weeks. Then without changing anything it worked — and didn't follow the constraints.”
A guess with no explanation, and a result you can't trust even when it succeeds.
“D9 can't be linearised — it multiplies two decisions. Here's the cell.”
The same input gives the same answer, and the answer is checked against your sheet before you rely on it.
“Problem could not be loaded. No model defined.”
You build the whole model by hand first, and it can still fail to load it.
Open the panel — the model is already there.
Read straight from the formulas you wrote, labelled in your own words.
Side by side
Every solver here does the maths. What separates them is how much of your account they ask for, and whether your figures ever leave your spreadsheet.
| Plumline | Typical alternative | |
|---|---|---|
| Reads the model for you | Yes | You define it by hand |
| Checks the answer in your sheet | Yes | — |
| Runs without a server | Always | Often queues on theirs |
| Access to your Drive | None | Sometimes full Drive |
| Linear & integer | Both | Varies |
| Price | Free | Free to ~£3/mo |
Capabilities vary by add-on and change over time; check each listing for its current terms.
Questions
No. There is no Plumline server. The whole calculation runs inside your own spreadsheet through Google Apps Script — no analytics, no cookies, no third-party requests. Plumline can see the spreadsheet it's installed in and nothing else: not your Drive, not your other files.
Linear and integer optimisation: production planning, purchasing, blending, staffing rotas, transport volumes, budget allocation — any problem shaped as “how much of each, given these limits”. It does not solve genuinely non-linear models (a decision multiplied by another decision), and it tells you plainly when it meets one.
Two: to read and write the spreadsheet it's installed in, and to show its side panel. Google adds an email and profile permission to every Marketplace listing by default; Plumline neither requests nor uses them. It asks for nothing else — no Drive, no Gmail, no external service.
The free tier handles models up to 50 decision variables and 20 limits, which covers the great majority of real spreadsheet problems. Because it runs inside Sheets rather than queuing on a server, there's no waiting in line and no 30-second server cut-off.
It's free.
Plumline
A free add-on for Google Sheets. Reads your model, solves it, and proves the result against your own formulas.