McpErrorCode.cs

namespace ModelContextProtocol;

/// <summary>
/// Represents standard JSON-RPC error codes as defined in the MCP specification.
/// </summary>
public enum McpErrorCode
{
    /// <summary>
    /// Indicates that the requested resource could not be found.
    /// </summary>
    /// <remarks>
    /// This error should be used when a resource URI does not match any available resource on the server.
    /// It allows clients to distinguish between missing resources and other types of errors.
    /// </remarks>
    ResourceNotFound = -32002,

    /// <summary>
    /// Indicates that URL-mode elicitation is required to complete the requested operation.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This error is returned when a server operation requires additional user input through URL-mode elicitation
    /// before it can proceed. The error data must include the `data.elicitations` payload describing the pending
    /// elicitation(s) for the client to present to the user.
    /// </para>
    /// <para>
    /// Common scenarios include OAuth authorization and other out-of-band flows that cannot be completed inside
    /// the MCP client.
    /// </para>
    /// </remarks>
    UrlElicitationRequired = -32042,

    /// <summary>
    /// Indicates that the JSON payload does not conform to the expected Request object structure.
    /// </summary>
    /// <remarks>
    /// The request is considered invalid if it lacks required fields or fails to follow the JSON-RPC protocol.
    /// </remarks>
    InvalidRequest = -32600,

    /// <summary>
    /// Indicates that the requested method does not exist or is not available.
    /// </summary>
    /// <remarks>
    /// <para>
    /// In MCP, this error is returned when a request is made for a method that requires a capability
    /// that has not been declared. This can occur in either direction:
    /// </para>
    /// <list type="bullet">
    /// <item><description>A server returning this error when the client requests a capability it doesn't support
    /// (for example, requesting completions when the <c>completions</c> capability was not advertised).</description></item>
    /// <item><description>A client returning this error when the server requests a capability it doesn't support
    /// (for example, requesting roots when the client did not declare the <c>roots</c> capability).</description></item>
    /// </list>
    /// </remarks>
    MethodNotFound = -32601,

    /// <summary>
    /// Indicates that the request parameters are invalid at the protocol level.
    /// </summary>
    /// <remarks>
    /// <para>
    /// In MCP, this error is returned for protocol-level parameter validation failures in various contexts:
    /// </para>
    /// <list type="bullet">
    /// <item><description><b>Tools</b>: Unknown tool name or invalid protocol-level tool arguments.</description></item>
    /// <item><description><b>Prompts</b>: Unknown prompt name or missing required protocol-level arguments.</description></item>
    /// <item><description><b>Pagination</b>: Invalid or expired cursor values.</description></item>
    /// <item><description><b>Logging</b>: Invalid log level.</description></item>
    /// <item><description><b>Tasks</b>: Invalid or nonexistent task ID or invalid cursor.</description></item>
    /// <item><description><b>Elicitation</b>: Server requests an elicitation mode not declared in client capabilities.</description></item>
    /// <item><description><b>Sampling</b>: Missing tool result or tool results mixed with other content.</description></item>
    /// </list>
    /// <para>
    /// Note: Application-layer validation errors within tool/prompt/resource arguments should be reported as execution errors
    /// (for example, via <see cref="Protocol.CallToolResult.IsError"/>) rather than as protocol errors, allowing language
    /// models to receive error feedback and self-correct.
    /// </para>
    /// </remarks>
    InvalidParams = -32602,

    /// <summary>
    /// Indicates that an internal error occurred while processing the request.
    /// </summary>
    /// <remarks>
    /// This error is used when the endpoint encounters an unexpected condition that prevents it from fulfilling the request.
    /// </remarks>
    InternalError = -32603,

    /// <summary>
    /// Indicates that the JSON received could not be parsed.
    /// </summary>
    /// <remarks>
    /// This error occurs when the input contains malformed JSON or incorrect syntax.
    /// </remarks>
    ParseError = -32700,
}