Add MCP server project exposing DAX formatting over stdio

src/Dax.Formatter.McpServer/Dax.Formatter.McpServer.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RootNamespace>Dax.Formatter.McpServer</RootNamespace>
+    <AssemblyName>Dax.Formatter.McpServer</AssemblyName>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="ModelContextProtocol" Version="1.2.0" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.7" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Dax.Formatter\Dax.Formatter.csproj" />
+  </ItemGroup>
+
+</Project>

src/Dax.Formatter.McpServer/FormatDaxTool.cs

@@ -0,0 +1,84 @@
+namespace Dax.Formatter.McpServer;
+
+using Dax.Formatter;
+using Dax.Formatter.Models;
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+using System.Reflection;
+
+[McpServerToolType]
+internal static class FormatDaxTool
+{
+    [McpServerTool(
+        Name = "format_dax",
+        Title = "Format DAX expressions",
+        ReadOnly = true,
+        Idempotent = true,
+        OpenWorld = true,
+        Destructive = false)]
+    [Description("""
+        Formats DAX (Data Analysis Expressions) code. DAX comments are preserved. Supports both DAX queries and DAX expressions.
+
+        WHEN TO CALL:
+        - The user asks to format, beautify, prettify or normalize DAX code.
+
+        RETURNS:
+        An array of responses, one per input in the same order:
+        {
+          Formatted: string,
+          Errors: [{ Line: int, Column: int, Message: string }]
+        }
+        A format failure (invalid DAX) results in null `Formatted` and a non-empty `Errors` array.
+        A successful format results in a non-null `Formatted` and an empty or null `Errors` array.
+
+        NOTE:
+        This tool calls an external HTTP service. Always batch multiple snippets
+        in a single call — looping the tool wastes round-trips and is rate-limited upstream.
+        """)]
+    public static async Task<DaxFormatterResponse[]> FormatDax(
+        IDaxFormatterClient client,
+        [Description("""
+            The DAX expressions to format. Each array element must be a complete,
+            independent piece of DAX code — either a DAX query or a DAX expression.
+            """)]
+        string[] expressions,
+        [Description("List separator character.")]
+        char listSeparator = ',',
+        [Description("Decimal separator character.")]
+        char decimalSeparator = '.',
+        [Description("""
+            Controls how arguments and sub-expressions are wrapped across lines.
+            - 'LongLine': keeps arguments compact horizontally where readable.
+            - 'ShortLine': breaks each argument onto its own line for maximum vertical clarity.
+            """)]
+        DaxFormatterLineStyle lineStyle = DaxFormatterLineStyle.LongLine,
+        [Description($"""
+            Controls spacing between function names and their opening parentheses.
+            - 'SpaceAfterFunction': adds a space for readability, e.g. 'SUM (x)'.
+            - 'NoSpaceAfterFunction': removes the space for compactness, e.g. 'SUM(x)'.
+            """)]
+        DaxFormatterSpacingStyle spacingStyle = DaxFormatterSpacingStyle.SpaceAfterFunction,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(expressions);
+
+        if (expressions.Length == 0)
+            return [];
+
+        var request = new DaxFormatterMultipleRequest();
+        {
+            // Set formatting options
+            request.DecimalSeparator = decimalSeparator;
+            request.ListSeparator = listSeparator;
+            request.MaxLineLength = lineStyle;
+            request.SkipSpaceAfterFunctionName = spacingStyle;
+            // Add caller info
+            request.CallerApp = "Dax.Formatter.McpServer";
+            request.CallerVersion = typeof(Program).Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion;
+        }
+        request.Dax.AddRange(expressions);
+
+        var responses = await client.FormatAsync(request, cancellationToken).ConfigureAwait(false);
+        return [.. responses];
+    }
+}

src/Dax.Formatter.McpServer/Program.cs

@@ -0,0 +1,57 @@
+using Dax.Formatter;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using System.Reflection;
+
+var builder = Host.CreateApplicationBuilder(args);
+
+builder.Logging.ClearProviders();
+builder.Logging.AddConsole(options => options.LogToStandardErrorThreshold = LogLevel.Trace);
+
+builder.Services.AddSingleton<IDaxFormatterClient, DaxFormatterClient>();
+builder.Services
+    .AddMcpServer(ConfigureMcpServerOptions)
+    .WithStdioServerTransport()
+    .WithToolsFromAssembly();
+
+await builder.Build().RunAsync();
+
+static void ConfigureMcpServerOptions(ModelContextProtocol.Server.McpServerOptions options)
+{
+    options.ServerInfo = new ModelContextProtocol.Protocol.Implementation
+    {
+        Name = "dax-formatter-mcp",
+        Version = typeof(Program).Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion ?? "0.0.0",
+        WebsiteUrl = "https://www.daxformatter.com"
+    };
+    options.ServerInstructions = """
+        # DAX Formatter MCP Server
+
+        ## Core Purpose
+
+        This server formats DAX (Data Analysis Expressions) source code for Microsoft
+        Power BI, Analysis Services, and Tabular models. It is the canonical wrapper
+        for the SQLBI daxformatter.com web service.
+
+        ## Strict Behavioral Rules
+
+        ### 1. Tool Selection
+
+        - No bypass: when DAX needs formatting, you MUST use this server's tools.
+          NEVER call the daxformatter.com HTTP endpoint directly.
+          This server is the single canonical channel for DAX formatting.
+
+        ### 2. Code Integrity
+
+        - Pass input as-is: the user's DAX is the authoritative source. You MUST
+          send it to the tool exactly as provided without altering the string in any way.
+          You MAY propose or apply changes only when the user has explicitly asked you to do so.
+
+        ### 3. Surface Errors
+
+        - Relay verbatim: if the formatter reports errors, you MUST pass them to
+          the user exactly as received including all details. They are diagnostic
+          information the user needs to fix the code.
+        """;
+}

src/Dax.Formatter.sln

@@ -7,6 +7,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Dax.Formatter", "Dax.Format
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Dax.Formatter.Tests", "Dax.Formatter.Tests\Dax.Formatter.Tests.csproj", "{44162C15-9AC7-406F-B1A4-1A49E73F962B}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Dax.Formatter.McpServer", "Dax.Formatter.McpServer\Dax.Formatter.McpServer.csproj", "{D839ACC9-427A-40AC-81FD-1DC4352FA019}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -21,6 +23,10 @@ Global
 		{44162C15-9AC7-406F-B1A4-1A49E73F962B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{44162C15-9AC7-406F-B1A4-1A49E73F962B}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{44162C15-9AC7-406F-B1A4-1A49E73F962B}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D839ACC9-427A-40AC-81FD-1DC4352FA019}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D839ACC9-427A-40AC-81FD-1DC4352FA019}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D839ACC9-427A-40AC-81FD-1DC4352FA019}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D839ACC9-427A-40AC-81FD-1DC4352FA019}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE