ec4c732632Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
307 lines
15 KiB
C#
307 lines
15 KiB
C#
using Microsoft.Extensions.AI;
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using Microsoft.Extensions.DependencyInjection;
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using ModelContextProtocol.Protocol;
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using System.Diagnostics.CodeAnalysis;
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using System.Text.Json;
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namespace ModelContextProtocol.Server;
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/// <summary>
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/// Indicates that a method should be considered an <see cref="McpServerTool"/>.
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/// </summary>
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/// <remarks>
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/// <para>
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/// This attribute is applied to methods that should be exposed as tools in the Model Context Protocol. When a class
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/// containing methods marked with this attribute is registered with McpServerBuilderExtensions,
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/// these methods become available as tools that can be called by MCP clients.
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/// </para>
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/// <para>
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/// When methods are provided directly to <see cref="M:McpServerTool.Create"/>, the attribute is not required.
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/// </para>
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/// <para>
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/// By default, parameters are sourced from the <see cref="CallToolRequestParams.Arguments"/> dictionary, which is a collection
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/// of key/value pairs, and are represented in the JSON schema for the function, as exposed in the returned <see cref="McpServerTool"/>'s
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/// <see cref="McpServerTool.ProtocolTool"/>'s <see cref="Tool.InputSchema"/>. Those parameters are deserialized from the
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/// <see cref="JsonElement"/> values in that collection. There are a few exceptions to this:
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/// <list type="bullet">
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/// <item>
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/// <description>
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/// <see cref="CancellationToken"/> parameters are automatically bound to a <see cref="CancellationToken"/> provided by the
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/// <see cref="McpServer"/> and that respects any <see cref="CancelledNotificationParams"/>s sent by the client for this operation's
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/// <see cref="RequestId"/>. The parameter is not included in the generated JSON schema.
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/// </description>
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/// </item>
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/// <item>
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/// <description>
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/// <see cref="IServiceProvider"/> parameters are bound from the <see cref="RequestContext{CallToolRequestParams}"/> for this request,
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/// and are not included in the JSON schema.
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/// </description>
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/// </item>
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/// <item>
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/// <description>
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/// <see cref="McpServer"/> parameters are not included in the JSON schema and are bound directly to the <see cref="McpServer"/>
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/// instance associated with this request's <see cref="RequestContext{CallToolRequestParams}"/>. Such parameters may be used to understand
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/// what server is being used to process the request, and to interact with the client issuing the request to that server.
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/// </description>
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/// </item>
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/// <item>
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/// <description>
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/// <see cref="IProgress{ProgressNotificationValue}"/> parameters accepting <see cref="ProgressNotificationValue"/> values
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/// are not included in the JSON schema and are bound to an <see cref="IProgress{ProgressNotificationValue}"/> instance manufactured
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/// to forward progress notifications from the tool to the client. If the client included a <see cref="ProgressToken"/> in their request,
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/// progress reports issued to this instance will propagate to the client as <see cref="NotificationMethods.ProgressNotification"/> notifications with
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/// that token. If the client did not include a <see cref="ProgressToken"/>, the instance will ignore any progress reports issued to it.
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/// </description>
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/// </item>
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/// <item>
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/// <description>
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/// When the <see cref="McpServerTool"/> is constructed, it may be passed an <see cref="IServiceProvider"/> via
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/// <see cref="McpServerToolCreateOptions.Services"/>. Any parameter that can be satisfied by that <see cref="IServiceProvider"/>
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/// according to <see cref="IServiceProviderIsService"/> will not be included in the generated JSON schema and will be resolved
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/// from the <see cref="IServiceProvider"/> provided to when the tool is invoked rather than from the argument collection.
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/// </description>
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/// </item>
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/// <item>
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/// <description>
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/// Any parameter attributed with <see cref="FromKeyedServicesAttribute"/> will similarly be resolved from the
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/// <see cref="IServiceProvider"/> provided when the tool is invoked rather than from the argument
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/// collection, and will not be included in the generated JSON schema.
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/// </description>
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/// </item>
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/// </list>
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/// </para>
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/// <para>
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/// All other parameters are deserialized from the <see cref="JsonElement"/>s in the <see cref="CallToolRequestParams.Arguments"/> dictionary,
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/// using the <see cref="JsonSerializerOptions"/> supplied in <see cref="McpServerToolCreateOptions.SerializerOptions"/>, or if none was provided,
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/// using <see cref="McpJsonUtilities.DefaultOptions"/>.
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/// </para>
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/// <para>
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/// In general, the data supplied via the <see cref="CallToolRequestParams.Arguments"/>'s dictionary is passed along from the caller and
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/// should thus be considered unvalidated and untrusted. To provide validated and trusted data to the invocation of the tool, consider having
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/// the tool be an instance method, referring to data stored in the instance, or using an instance or parameters resolved from the <see cref="IServiceProvider"/>
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/// to provide data to the method.
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/// </para>
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/// <para>
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/// The tool method is responsible for validating its own input arguments (e.g., checking required fields, value ranges, string lengths, or
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/// any other business rules). Data annotations such as <c>RequiredAttribute</c> and
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/// <c>MaxLengthAttribute</c> on parameter types influence the generated JSON schema exposed
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/// to clients, but they are not enforced at runtime by the SDK. Validation should be performed explicitly within the tool method.
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/// </para>
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/// <para>
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/// To signal an error (including validation failures) back to the client, either throw an <see cref="McpException"/>
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/// or return a <see cref="CallToolResult"/> with <see cref="CallToolResult.IsError"/> set to <see langword="true"/>.
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/// When a tool throws an <see cref="McpException"/>, its <see cref="Exception.Message"/> is included in the error result
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/// sent to the client. Throwing any other exception type also results in an error <see cref="CallToolResult"/>, but with
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/// a generic error message (to avoid leaking sensitive information). Alternatively, a tool can declare a return type of
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/// <see cref="CallToolResult"/> to have full control over both success and error responses.
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/// </para>
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/// <para>
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/// It is important to provide clear <see cref="System.ComponentModel.DescriptionAttribute"/> values on tool methods and their parameters.
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/// These descriptions are surfaced to AI models and help them determine when and how to use the tool, what values to pass for each parameter,
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/// and what constraints the parameters have. Well-written descriptions reduce incorrect tool invocations and improve the quality of
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/// model interactions.
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/// </para>
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/// <para>
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/// Return values from a method are used to create the <see cref="CallToolResult"/> that is sent back to the client:
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/// </para>
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/// <list type="table">
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/// <item>
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/// <term><see langword="null"/></term>
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/// <description>Returns an empty <see cref="CallToolResult.Content"/> list.</description>
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/// </item>
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/// <item>
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/// <term><see cref="AIContent"/></term>
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/// <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
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/// </item>
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/// <item>
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/// <term><see cref="string"/></term>
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/// <description>Converted to a single <see cref="TextContentBlock"/> object with its text set to the string value.</description>
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/// </item>
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/// <item>
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/// <term><see cref="ContentBlock"/></term>
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/// <description>Returned as a single-item <see cref="ContentBlock"/> list.</description>
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/// </item>
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/// <item>
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/// <term><see cref="IEnumerable{String}"/> of <see cref="string"/></term>
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/// <description>Each <see cref="string"/> is converted to a <see cref="ContentBlock"/> object with its text set to the string value.</description>
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/// </item>
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/// <item>
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/// <term><see cref="IEnumerable{AIContent}"/> of <see cref="AIContent"/></term>
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/// <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
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/// </item>
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/// <item>
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/// <term><see cref="IEnumerable{Content}"/> of <see cref="ContentBlock"/></term>
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/// <description>Returned as the <see cref="ContentBlock"/> list.</description>
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/// </item>
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/// <item>
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/// <term><see cref="CallToolResult"/></term>
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/// <description>Returned directly without modification.</description>
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/// </item>
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/// <item>
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/// <term>Other types</term>
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/// <description>Serialized to JSON and returned as a single <see cref="ContentBlock"/> object with <see cref="ContentBlock.Type"/> set to "text".</description>
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/// </item>
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/// </list>
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/// </remarks>
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[AttributeUsage(AttributeTargets.Method)]
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public sealed class McpServerToolAttribute : Attribute
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{
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// Defaults based on the spec
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private const bool DestructiveDefault = true;
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private const bool IdempotentDefault = false;
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private const bool OpenWorldDefault = true;
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private const bool ReadOnlyDefault = false;
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// Nullable backing fields so we can distinguish
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internal bool? _destructive;
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internal bool? _idempotent;
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internal bool? _openWorld;
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internal bool? _readOnly;
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internal ToolTaskSupport? _taskSupport;
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/// <summary>
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/// Initializes a new instance of the <see cref="McpServerToolAttribute"/> class.
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/// </summary>
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public McpServerToolAttribute()
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{
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}
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/// <summary>Gets the name of the tool.</summary>
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/// <remarks>If <see langword="null"/>, the method name is used.</remarks>
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public string? Name { get; set; }
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/// <summary>
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/// Gets or sets a human-readable title for the tool that can be displayed to users.
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/// </summary>
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/// <remarks>
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/// <para>
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/// The title provides a more descriptive, user-friendly name for the tool than the tool's
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/// programmatic name. It is intended for display purposes and to help users understand
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/// the tool's purpose at a glance.
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/// </para>
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/// <para>
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/// Unlike the tool name (which follows programmatic naming conventions), the title can
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/// include spaces, special characters, and be phrased in a more natural language style.
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/// </para>
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/// </remarks>
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public string? Title { get; set; }
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/// <summary>
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/// Gets or sets a value that indicates whether the tool might perform destructive updates to its environment.
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/// </summary>
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/// <value>
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/// <see langword="true"/> if the tool might perform destructive updates to its environment.
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/// <see langword="false"/> if the tool performs only additive updates.
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/// The default is <see langword="true"/>.
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/// </value>
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/// <remarks>
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/// This property is most relevant when the tool modifies its environment (ReadOnly = false).
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/// </remarks>
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public bool Destructive
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{
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get => _destructive ?? DestructiveDefault;
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set => _destructive = value;
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}
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/// <summary>
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/// Gets or sets a value that indicates whether calling the tool repeatedly with the same arguments
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/// has no additional effect on its environment.
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/// </summary>
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/// <value>
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/// <see langword="true"/> if calling the tool repeatedly with the same arguments
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/// has no additional effect on the environment; <see langword="false"/> if it does.
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/// The default is <see langword="false"/>.
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/// </value>
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/// <remarks>
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/// This property is most relevant when the tool modifies its environment (ReadOnly = false).
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/// </remarks>
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public bool Idempotent
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{
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get => _idempotent ?? IdempotentDefault;
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set => _idempotent = value;
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}
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/// <summary>
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/// Gets or sets a value that indicates whether this tool can interact with an "open world" of external entities.
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/// </summary>
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/// <value>
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/// <see langword="true"/> if the tool can interact with an unpredictable or dynamic set of entities (like web search).
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/// <see langword="false"/> if the tool's domain of interaction is closed and well-defined (like memory access).
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/// The default is <see langword="true"/>.
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/// </value>
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public bool OpenWorld
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{
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get => _openWorld ?? OpenWorldDefault;
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set => _openWorld = value;
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}
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/// <summary>
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/// Gets or sets a value that indicates whether this tool does not modify its environment.
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/// </summary>
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/// <value>
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/// <see langword="true"/> if the tool only performs read operations without changing state.
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/// <see langword="false"/> if the tool might make modifications to its environment.
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/// The default is <see langword="false"/>.
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/// </value>
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/// <remarks>
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/// Read-only tools do not have side effects beyond computational resource usage.
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/// They don't create, update, or delete data in any system.
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/// </remarks>
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public bool ReadOnly
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{
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get => _readOnly ?? ReadOnlyDefault;
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set => _readOnly = value;
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}
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/// <summary>
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/// Gets or sets a value that indicates whether the tool should report an output schema for structured content.
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/// </summary>
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/// <value>
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/// The default is <see langword="false"/>.
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/// </value>
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/// <remarks>
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/// When enabled, the tool will attempt to populate the <see cref="Tool.OutputSchema"/>
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/// and provide structured content in the <see cref="CallToolResult.StructuredContent"/> property.
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/// </remarks>
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public bool UseStructuredContent { get; set; }
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/// <summary>
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/// Gets or sets the source URI for the tool's icon.
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/// </summary>
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/// <remarks>
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/// <para>
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/// This value can be an HTTP/HTTPS URL pointing to an image file or a data URI with base64-encoded image data.
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/// When specified, a single icon will be added to the tool.
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/// </para>
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/// <para>
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/// For more advanced icon configuration (multiple icons, MIME type specification, size characteristics),
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/// use <see cref="McpServerToolCreateOptions.Icons"/> when creating the tool programmatically.
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/// </para>
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/// </remarks>
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public string? IconSource { get; set; }
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/// <summary>
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/// Gets or sets the task support configuration for the tool.
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/// </summary>
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/// <value>
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/// A <see cref="ToolTaskSupport"/> value indicating how the tool supports task-based invocation.
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/// The default value is <see cref="ToolTaskSupport.Forbidden"/>.
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/// </value>
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/// <remarks>
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/// <para>
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/// When set to <see cref="ToolTaskSupport.Forbidden"/>, clients must not attempt to invoke the tool as a task.
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/// When set to <see cref="ToolTaskSupport.Optional"/>, clients may invoke the tool as a task or as a normal request.
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/// When set to <see cref="ToolTaskSupport.Required"/>, clients must invoke the tool as a task.
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/// </para>
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/// <para>
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/// If this property is not explicitly set on the attribute, the task support behavior will be determined
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/// automatically based on the tool's characteristics (e.g., async methods default to <see cref="ToolTaskSupport.Optional"/>).
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/// </para>
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/// </remarks>
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[Experimental(Experimentals.Tasks_DiagnosticId, UrlFormat = Experimentals.Tasks_Url)]
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public ToolTaskSupport TaskSupport
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{
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get => _taskSupport ?? ToolTaskSupport.Forbidden;
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set => _taskSupport = value;
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}
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}
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