Your formulas. Your rules.
Write Lua functions, call them like built-ins.
Sandboxed. Deterministic. Verifiable.
Custom logic inside the sandbox — not an escape hatch from it.
If it runs, it runs the same way every time.
The problem with custom code in spreadsheets
Most spreadsheet "custom code" is stateful, side-effectful, and impossible to verify.
VBA macros read the clock. Python add-ins call APIs. Excel lambdas compose, but can't enforce purity.
Once you allow time, randomness, or I/O, reproducibility is dead. The output depends on when you ran it, not what you ran.
Custom code in spreadsheets is where auditability goes to die.
VisiGrid takes a different approach: your code runs inside the same deterministic sandbox as everything else.
Write Lua, call in formulas
=ACCRUED_INTEREST(B6, C6, D6) works like any built-in. No macros. No add-ins. No special mode.
Define a function in Lua. VisiGrid registers it alongside the 181 built-in functions. It appears in autocomplete, works in formulas, and evaluates during recalculation.
One file. One language. Functions available in every sheet.
Sandboxed by default
No global mutation. No randomness. No I/O. Hard instruction limits.
Custom functions run in a Lua sandbox with the same constraints as built-in functions: pure input, pure output, no side effects.
If it runs, it runs the same way every time. That's not a limitation — it's the entire point.
What travels with the workbook
functions.lua lives on your machine, in ~/.config/visigrid/, not inside the workbook. Someone who opens your file without it sees the values you last saved, and Unknown function if a cell recalculates.
The workbook fingerprint covers inputs and formulas. It records that a cell calls =ACCRUED_INTEREST(…), not what the function does, so changing functions.lua does not change it. If two people must agree on a result, they must agree on functions.lua too.
When the logic has to travel with the file, put it in the cell: =LUA("…", B2, C2) keeps its code in the formula, runs in the same sandbox, and is saved with the workbook and covered by its fingerprint.
When it matters
Finance
Accrual calculations, day-count conventions, custom pricing models — written once, in one readable place.
Compliance
Domain rules a reviewer can read line by line, instead of a nested formula copied down a column.
Domain-specific calculations
Engineering formulas, scientific models, industry-standard computations.
Logic that travels
Put a rule in an <code class="font-mono">=LUA</code> cell and it goes wherever the workbook goes, covered by its fingerprint.
Try it in 60 seconds
Three steps. No setup beyond the app itself.
Create the functions file
Paste a function
-- Accrued interest (actual/365)
function ACCRUED_INTEREST(principal, rate, days)
return principal * rate * days / 365
endUse it in a formula
Open VisiGrid. Type =ACCRUED_INTEREST(1000000, 0.0425, 92) in any cell. It evaluates like a built-in.
It also runs headless: vgrid loads the same functions.lua. The file stays on your machine, so to send a rule along with a workbook, use an =LUA cell.
Build your own formulas
Custom functions are included in VisiGrid Free. Write Lua, call it in formulas.