Formidable 2.0.0

Formidable

Form validation for Blazor, built on FluentValidation — profiles, progressive disclosure, row-stable collections, and one wire format shared by client and server.

I wrote it because the layer between Blazor's EditForm and FluentValidation is one I kept rebuilding by hand, one client form at a time. This is that layer, built once and covered by tests, running a real project's forms today.

What it is

• Draft and Submit from one validator — two lifecycles ship built in: a lenient Draft profile for save-as-you-go, a strict Submit profile for the real thing, both defined once in the same FluentValidation class. Wizard steps and approval stages are custom profiles over that same definition.
• A headless component kit — FormidableForm, FormidableField, FormidableFieldMessage, and FormidableSummary own the EditContext and render the validator's verdict. The library ships no CSS, so the kit drops into a UI library, a design system, or plain HTML.
• One validator, client and server — the same FluentValidation rules run in the browser and again on the server, and the server's ValidationProblemDetails response applies straight into the engine, so a rejected save lights up the exact fields inline.
• Progressive disclosure — a message waits until the visitor has earned it. A field nobody has touched stays silent whatever its rules say; once they have engaged it, it tells them what would actually block the save. A form opened on a saved draft says what those loaded values have already earned in one call. At submit, which errors show is decided by what is on screen at that moment, and a defensive gate catches the case where every failure would otherwise go unseen.
• Warnings and infos that never block: a FluentValidation check followed by .WithSeverity(Severity.Warning) or Severity.Info fails as a warning or an info. Either one shows in the same field messages and summary as an error, with its own CSS class, but only errors stop a submit.
• Collections that keep their errors — a message on a row object belongs to the object, not to the row number, so adding, removing, and reordering rows can never move its error onto the wrong line.

Packages

• Formidable — validation profiles, ProfiledValidator/DraftSubmitValidator, the model validator seam, ValidationIssue/ValidationReport, INormalizableModel. FluentValidation plus Microsoft.Extensions.DependencyInjection.Abstractions, no Blazor dependency.
• Formidable.Blazor — the validation engine (EditContext integration, field registry, validation flows) and the headless component kit.
• Formidable.AspNetCore — minimal-API endpoint filter and MVC action filter, returning ValidationProblemDetails in the same path format the Blazor client consumes.

Quickstart

Install the Blazor package:

dotnet add package Formidable.Blazor

Register it and your FluentValidation validators in Program.cs, using directives included:

using FluentValidation;
using Formidable.Blazor;

builder.Services.AddFormidableBlazor();
builder.Services.AddScoped<IValidator<QuickContact>, QuickContactValidator>();

Add one line to _Imports.razor so the components resolve:

@using Formidable.Blazor

Then wrap a model in FormidableForm and let FormidableInputText, FormidableFieldMessage, and FormidableSummary render the validator's verdict. That is a working form, on any page with an interactive render mode (every page of a standalone WebAssembly app, or a Blazor Web App page carrying @rendermode InteractiveServer, @rendermode InteractiveWebAssembly or @rendermode InteractiveAuto).

In a Blazor Web App (the two-project template), add the same two lines to both Program.cs files: pages prerender and can run on the server, and a validator registered only in the .Client project is invisible there. The quickstart (https://github.com/xfunc-pty-ltd/formidable/blob/main/docs/quickstart.md) has the exact settings per render mode.

Links

The full documentation, the runnable sample app, and every recipe live in the repository:

• Repository: https://github.com/xfunc-pty-ltd/formidable
• Documentation index: https://github.com/xfunc-pty-ltd/formidable/tree/main/docs
• Recipes (behaviour to configuration): https://github.com/xfunc-pty-ltd/formidable/blob/main/docs/recipes.md
• Live demo: https://xfunc-pty-ltd.github.io/formidable/
• Issues and contributions: https://github.com/xfunc-pty-ltd/formidable/blob/main/CONTRIBUTING.md

Licensed under the MIT License.