Optimisation for Google Sheets
You have a spreadsheet, a goal, and a few limits. Plumline finds the best way to hit that goal without breaking a limit, writes it into your sheet, and shows you the number checks out. No setup, no jargon.
A worked example · drag to change the limits
this demo runs in your browser. the real add-on runs in your sheet.
Nothing to set up
Open the panel and your problem is already laid out. Plumline spots which cells you're deciding, which total you're chasing, and which limits it has to respect. It labels them with the words you typed, not with cell references like B2:B4. Read something wrong? Fix it in a click. You never start from a blank form, and you never get "no model defined".
The part that matters
Most tools hand you a number and expect you to believe it. But a solver's whole point is that you didn't know the answer, so how would you check it? Plumline writes its answer into your sheet, lets Google Sheets add it up on its own, and shows you the two totals match. It also lists every limit with how much you used and how much is spare, so you can see exactly what's holding the result back.
When it can't
Read the reviews of the other solvers and you'll see the same story: it failed, gave no reason, and someone lost an afternoon second-guessing their own spreadsheet. Or worse, it worked one day and quietly ignored a limit the next. Plumline points at the exact cell and explains the problem in plain words. Same input, same answer, every time.
Whole numbers when you need them
You can't ship 1.67 trucks or roster 4.5 people. Tick whole units only and Plumline looks for the best whole-number answer, which isn't the same as rounding the fractional one. Try it above: drop the hours to 30. The fractional answer makes 1.67 of product C; the whole-number answer reshuffles the whole plan instead of rounding that 1.67 up or down. And if it runs out of time, it's honest about it, telling you it's the best found so far, not necessarily the best possible.
Why it's different
We didn't invent these frustrations. They're pulled from the actual 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
They all do the maths. The question worth asking is how much of your Google account each one wants, and whether your numbers ever leave the sheet.
| 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.
For the people who know what a solver is
If you already speak in objectives and constraints, here's exactly what the engine does, and where its edges are. No marketing in this part.
| Method | Plumline | What it means |
|---|---|---|
| Model building | Formula parsing | Reads the algebra out of your cells. No iterative probing, no rebuild step. |
| Linear programs | Two-phase simplex | Bland's rule, so it can't cycle. Detects infeasible and unbounded. |
| Integer programs | Branch & bound | On top of the simplex. Says "best found" if it runs out of time rather than pretending. |
| Sensitivity | Shadow prices | For every binding limit, the marginal value of one more unit. The report the paid tools charge for. |
| Self-check | Round-trip | Writes the answer, lets Sheets recompute, confirms the totals agree. |
Honesty is the whole pitch, so the limits are stated plainly:
Questions
No. There's no Plumline server for it to go to. Everything happens inside your own spreadsheet through Google Apps Script. No analytics, no cookies, no outside requests. Plumline can see the one sheet you opened it in, and nothing else. Not your Drive, not your other files.
Anything shaped like "how much of each, given these limits": production runs, purchasing, blends and mixes, staff rotas, delivery loads, splitting a budget across channels. It handles both fractional and whole-number answers. It can't solve truly non-linear problems, like one decision multiplied by another, and it'll tell you straight when it hits one.
Two. One to read and write the sheet it's installed in, one to show its side panel. Google tacks an email and profile permission onto every Marketplace listing automatically; Plumline doesn't ask for those and doesn't use them. Nothing else: no Drive, no Gmail, no outside connection.
The free version handles up to 50 decisions and 20 limits, which covers most everyday spreadsheet problems comfortably. And because it runs inside Sheets instead of queuing on someone's server, there's no waiting your turn and no cut-off halfway through.
It's free.
Plumline
A free Google Sheets add-on that reads your model, solves it, and proves the result against your own formulas.