Results and Content

Handlers build their answers with these helpers, all from MCP.Server.

Tool results

A tool handler returns TMCPToolResult; build it with one of:

function MCPTextResult(const AText: string): TMCPToolResult;
function MCPErrorResult(const AText: string): TMCPToolResult;
function MCPStructuredResult(const AText: string;
  AStructured: TJSONData): TMCPToolResult;
function MCPStructuredResult(const AText: string;
  AObj: TMCPArgs): TMCPToolResult;
function MCPImageResult(const ABase64,
  AMimeType: string): TMCPToolResult;
function MCPImageResult(const AData: TBytes;
  const AMimeType: string): TMCPToolResult;

• MCPTextResult — one text content block.
• MCPErrorResult — the same shape with isError: true: the in-band error channel a model reads and corrects against. Use it for everything the caller did wrong; reserve exceptions for what went wrong in the server (they become isError results too, with messages subject to redaction).
• MCPStructuredResult — text plus structuredContent. The TJSONData overload takes ownership of the data you pass; the TMCPArgs overload serializes an instance of a typed output class and frees it (see Schemas).
• MCPImageResult — one image content block (type, data, mimeType). The string overload takes data that is already base64 (the same contract as MCPBlobContents); the TBytes overload base64-encodes the raw bytes itself. AMimeType is the image's IANA media type (image/png, image/jpeg, …) and goes on the wire verbatim — the spec names no enumeration, so the handler owns that choice.

The MRTR variant MCPInputRequired is documented with the other client-request builders in Client requests.

Resource contents

Resource readers return a TJSONArray of contents entries:

function MCPTextContents(const AUri, AMimeType,
  AText: string): TJSONArray;
function MCPBlobContents(const AUri, AMimeType,
  ABase64: string): TJSONArray;

Each returns a single-entry array — text or base64-encoded binary — echoing the URI the client asked for. See Resources.

Prompt messages

A prompt handler returns a TJSONArray of messages:

function MCPPromptMessage(const ARole, AText: string): TJSONObject;
function MCPUserMessage(const AText: string): TJSONObject;
function MCPAssistantMessage(const AText: string): TJSONObject;
function MCPMessages(const AMessages: array of TJSONObject): TJSONArray;

The MRTR-capable prompt shape returns TMCPPromptResult instead; wrap a message array with:

function MCPPromptMessagesResult(AMessages: TJSONArray): TMCPPromptResult;

or answer an input round with MCPPromptInputRequired — see Client requests. Guide: Prompts.

In-request notifications

Emitted through the request context, written to the client before the response; both are no-ops unless the request opted in:

procedure MCPReportProgress(const ACtx: TMCPRequestContext;
  AProgress: Double; ATotal: Double = -1; const AMessage: string = '');
procedure MCPLogMessage(const ACtx: TMCPRequestContext;
  const ALevel, AData: string; const ALogger: string = '');

Levels are RFC 5424 (debug … emergency); gating and delivery are described in Progress and logging.