SharePoint form validation rules that actually hold

Every SharePoint form ships with a validation story somebody thought was finished. Then a manager imports forty rows from a spreadsheet, a flow writes an item with an empty required field, and somebody types "ASAP" into a date box. The rules were real — they were just all in one layer.

There are three layers, and each catches mistakes the others cannot. Build all three and the list stays clean regardless of how items arrive.

Layer 1 — Field rules in the form

These run while the respondent is still on the page, which makes them the only layer that can actually teach someone the right answer. In Smart Forms each question carries its own rules: required, minimum and maximum for numbers, character limits for text, and format checks on email, phone and URL questions.

• Set numeric bounds on anything that has a real-world range — hours, quantities, percentages.
• Use the typed question rather than a text box: a date question, a currency question, a person picker.
• Keep the message specific. "Enter a whole number of hours between 1 and 40" beats "Invalid value".

Layer 2 — Branching, so bad answers are impossible

The cheapest validation is the question you never ask. Instead of adding an "N/A" choice to a question that only applies to contractors, put the question behind a rule: show when Employment type is Contractor. The data comes back with no N/A rows to filter out, and the form gets shorter for everyone else.

Branching also solves conditional required, which the built-in list form cannot do at all. Mark the question required and hide it behind a rule — it is enforced only on the path where it is asked. See branching logic in a SharePoint form for the rule syntax.

Layer 3 — Column validation on the list

This is the layer people skip, and it is the only one that holds when the write does not come from the form. In List settings:

• Column validation for single-column rules, on the column itself. It can only reference its own column.
• List validation for cross-column rules, under List settings → Validation settings. This is where =[End Date]>=[Start Date] belongs.

Both apply to every write path: the form, an Excel import, Power Automate, the REST API, and someone editing in grid view. Write the user message on the validation settings page — SharePoint shows it verbatim.

The rules worth setting on every form

1. Dates that describe a period get a list validation formula ensuring the end is not before the start.
2. Any "other, please specify" text box is required only when Other is selected.
3. Free-text fields that feed a report get a character limit, so the column stays readable in a view.
4. Money and quantity fields are typed as number or currency, never text, and carry a maximum.
5. Anything identifying a person is a person picker, so it resolves against Entra ID instead of spelling.

Test it with three bad submissions

Before you share the link, submit the form three times deliberately wrong: completely empty, wrong types in every box, and a submission where every individual field is valid but the combination is not. The third one is the test that finds the missing list validation formula.

Then run the pre-flight check in the designer. It flags unreachable questions, required fields hidden by branching rules, and rules that contradict each other — the three failures that only appear after the form is live.

Related

• SharePoint list form customization: every option
• Route form responses to Teams and email
• SharePoint forms: complete reference
• SharePoint Smart Forms