> ## Documentation Index > Fetch the complete documentation index at: https://si.easyaf.dev/llms.txt > Use this file to discover all available pages before exploring further. # Analyzers > Roslyn diagnostics that catch broken MCP forms while you type—unmappable properties, colliding wire names, and invalid lambdas. MCP form elicitation is easy to get slightly wrong: a nested object on `From()`, two properties that camelCase to the same name, a lambda that isn’t `x => x.Email`. Runtime skips or throws. The analyzers in **McpEssentials.Core** turn those mistakes into IDE squiggles and `dotnet build` diagnostics. They fire on [`FormElicitation.From()`](https://si.easyaf.dev/mcpessentials/guides/form-elicitation) and on expression starters (`Exclude`, `String`, `Email`, …). String-named `Create()` fields are whatever you add, so they are not analyzed. > [card] Ships in Core > > `dotnet add package McpEssentials.Core` is enough. No extra package for everyday use. > [card] Six IDs > > MCPESS001–006. Warnings, errors, and one info. All in the Usage category. > [card] Same chain > > `.Exclude(x => x.Home)` on the `From` call that seeded `Home` suppresses MCPESS001 for that property. ## Install > [tab] With Core > > Core already packs `CloudNimble.McpEssentials.Analyzers.dll` under `analyzers/dotnet/cs`. Adding Core to a project enables the diagnostics. > > ```bash theme={"dark"} > dotnet add package McpEssentials.Core > ``` > [tab] Analyzers only > > Use `McpEssentials.Analyzers` when you want the analyzer assembly without taking Core as a runtime dependency, or to pin analyzer versions separately. > > ```bash theme={"dark"} > dotnet add package McpEssentials.Analyzers > ``` > [!TIP] > > Rebuild after adding Core. Roslyn loads analyzers from the package; a running IDE may need a restart before squiggles appear. ## What they watch **1. From a type** `FormElicitation.From("…")` and `new FormElicitationBuilder("…")`. Public instance properties are checked against the same mapping rules as runtime. **2. Expression starters** `Exclude`, `String`, `Email`, `Uri`, `Date`, `DateTime`, `Integer`, `Number`, `Boolean`, `Choice`, and `MultiChoice` when the first argument is a lambda. **3. The fluent chain** `Exclude` calls on the same expression as `From` are collected so skipped properties you already excluded do not warn. > [!NOTE] > > `FormElicitation.Create("…").String("filter")` is metadata-driven. There is no CLR property to inspect, so the analyzers stay quiet. That is the path for OData `$metadata` and other runtime catalogs. ## Diagnostics > [accordion] MCPESS001 — unmappable property > > **Warning.** `From()` skips public properties the MCP form schema cannot represent: nested objects, dictionaries, `TimeSpan`, `byte[]`, `string[]`, indexers, write-only and static members. > > ```csharp Warns theme={"dark"} > public class SignupForm > { > public string Name { get; set; } > public Address Home { get; set; } // skipped at runtime > } > > FormElicitation.From("Sign up"); > // MCPESS001: Property 'Home' on 'SignupForm' is skipped by FormElicitation.From. > ``` > > ```csharp Fixed theme={"dark"} > FormElicitation.From("Sign up") > .Exclude(x => x.Home); > ``` > > An empty type (no public properties) is a confirm dialog and does **not** warn. > [accordion] MCPESS002 — colliding wire names > > **Error.** Two properties camelCase to the same JSON name. Runtime throws `InvalidOperationException` at `From`. The analyzer fails the build instead. > > ```csharp Errors theme={"dark"} > public class CollisionForm > { > public string EmailAddress { get; set; } > public string emailAddress { get; set; } // both become emailAddress > } > > FormElicitation.From("m"); > // MCPESS002: Properties 'EmailAddress' and 'emailAddress' on 'CollisionForm' > // both map to form field 'emailAddress'. > ``` > > ```csharp Fixed theme={"dark"} > FormElicitation.From("m") > .Exclude(x => x.emailAddress); > ``` > [accordion] MCPESS003 — nested or invalid lambda > > **Error.** Expression starters and `Exclude` require a simple property access on the form type, the same rule as `FormElicitationProperty.From`. Nested members, method calls, and fields fail. > > ```csharp Errors theme={"dark"} > FormElicitation.From("m") > .Exclude(x => x.Address.City); // nested > > FormElicitation.From("m") > .String(x => x.Name.Trim()); // method > ``` > > ```csharp Fixed theme={"dark"} > FormElicitation.From("m") > .Exclude(x => x.Address) > .String(x => x.Name); > ``` > [accordion] MCPESS004 — Exclude of something that was never a field > > **Info.** `Exclude` of an unmappable property is a successful no-op at runtime. The analyzer tells you so you do not think you removed a field that was never seeded. > > ```csharp theme={"dark"} > public class Form > { > public string Name { get; set; } > public Address Home { get; set; } > } > > FormElicitation.From
("m").Exclude(x => x.Home); > // MCPESS004: Exclude of 'Home' does nothing because the property is not a supported form field > // MCPESS001 is suppressed for Home on this From call. > ``` > [accordion] MCPESS005 — From on a built-in > > **Warning.** `From()` expects a class or struct of public properties. `string`, primitives, enums, and arrays are not form DTOs. > > ```csharp Warns theme={"dark"} > FormElicitation.From("m"); > FormElicitation.From("m"); > FormElicitation.From("m"); > ``` > > ```csharp Fixed theme={"dark"} > FormElicitation.From("m"); > FormElicitation.Create("m").String("notes"); > ``` > [accordion] MCPESS006 — field added after Build > > **Warning.** `Build`, `ToXml`, `ToJson`, `ToDefinition`, and `ToInputRequest` seal the form. A later starter or `Exclude` on that local would throw at runtime. > > ```csharp Warns theme={"dark"} > var form = FormElicitation.Create("m").String("trackingNumber"); > form.Build(); > form.Integer("quantity"); // MCPESS006 > ``` > > ```csharp Fixed theme={"dark"} > var form = FormElicitation.Create("m") > .String("trackingNumber") > .Integer("quantity"); > form.Build(); > ``` ## Severity at a glance | Id | Severity | Default | Typical fix | | - | - | - | - | | MCPESS001 | Warning | On | `.Exclude(x => x.Prop)` or change the property type | | MCPESS002 | Error | On | Rename or Exclude one of the colliding properties | | MCPESS003 | Error | On | Use `x => x.Email`, not nested access | | MCPESS004 | Info | On | Drop the `Exclude`, or leave it as documentation | | MCPESS005 | Warning | On | Pass a form DTO, or use `Create()` | | MCPESS006 | Warning | On | Add every field before `Build` / `ToXml` / `ToJson` | ## Suppress a diagnostic Use this when the skip is deliberate and you do not want `.Exclude` on the chain. > [tab] Inline > > ```csharp theme={"dark"} > #pragma warning disable MCPESS001 > var form = FormElicitation.From("Continue"); > #pragma warning restore MCPESS001 > ``` > [tab] EditorConfig > > ```ini theme={"dark"} > [*.cs] > dotnet_diagnostic.MCPESS001.severity = suggestion > dotnet_diagnostic.MCPESS004.severity = none > ``` > [tab] Project > > ```xml theme={"dark"} > > $(NoWarn);MCPESS004 > > ``` > [!WARNING] > > Do not suppress MCPESS002 or MCPESS003. Those match runtime exceptions. A warning you understand (MCPESS001 on a DTO you do not own) is the usual candidate. ## What maps The analyzer uses the same rules as [`FormElicitation.From()`](https://si.easyaf.dev/mcpessentials/guides/form-elicitation). If Core would seed a field, MCPESS001 stays quiet. > [accordion] Seeded > > `string`, `Guid`, `char`, `Uri`, `DateOnly`, `DateTime`, `DateTimeOffset`, `bool`, integer types, `float` / `double` / `decimal`, enums, `[Flags]` enums, and sequences of enums (`TEnum[]`, `List`, `IEnumerable`). > [accordion] Skipped > > Nested objects, `Dictionary<,>`, `object`, `TimeSpan`, `byte[]`, `string[]`, `int[]`, indexers, write-only properties, static properties. ## Related > [card] [Form elicitation](https://si.easyaf.dev/mcpessentials/guides/form-elicitation.md) > > Fluent schemas, ElicitAsync, and parking a form on a task. > [card] [FormElicitation API](https://si.easyaf.dev/mcpessentials/api-reference/CloudNimble/McpEssentials/Core/Tasks/Elicitations/FormElicitation.md) > > `Create`, `From`, and `Bind`. > [card] [Authenticated tasks](https://si.easyaf.dev/mcpessentials/guides/authenticated-tasks.md) > > Isolation, identity factory, and the samples. > [card] [Stores](https://si.easyaf.dev/mcpessentials/guides/stores.md) > > Durable providers that persist the parked form. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.