AT-360 Added Diagram Chat Functionality To Mermaid/sdk So MCP Server Can Directly Access Mermaid AI by Prashant-7718 · Pull Request #43 · Mermaid-Chart/plugins

Prashant-7718 · 2026-03-31T08:05:18Z

This pull request adds a diagramChat method to the @mermaidchart/sdk, enabling external clients such as MCP servers to chat directly with Mermaid AI without handling streaming internals themselves.

These changes also expose the necessary types (DiagramChatRequest, DiagramChatResponse) so consumers get full TypeScript support for the new chat capability.

New diagramChat method in SDK:

Added MermaidChart.diagramChat() which posts a single user message to the collab chat endpoint with autoFetchHistory: true, so callers never need to track or resend previous messages.
Used responseType: 'text' on the axios request to buffer the full Vercel AI data-stream body as a plain string, then parsed it with two dedicated helpers: parseVercelAIStreamText (extracts AI reply from 0: lines) and parseVercelAIStreamData (extracts documentChatThreadID from 2: data lines).
Returns a clean { text, documentChatThreadID, documentID } object — the resolved thread ID falls back to the caller-supplied one if the backend did not return a new one.
Added DiagramChatRequest and DiagramChatResponse interfaces to types.ts covering message, code, documentID, documentChatThreadID, and the full response shape.

…at with mermaid ai

vercel · 2026-03-31T08:05:23Z

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Copilot

Pull request overview

Adds SDK support for a new Mermaid AI “diagram chat” endpoint so consumers (e.g., an MCP server) can send a user prompt + optional diagram context and receive streamed AI output.

Changes:

Added /rest-api/openai/chat URL constant.
Introduced DiagramChatRequest / DiagramChatResponse public types.
Implemented MermaidChart.diagramChat() including parsing of Vercel AI SDK data-stream output.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
packages/sdk/src/urls.ts	Adds the REST URL for the new OpenAI chat endpoint.
packages/sdk/src/types.ts	Defines request/response types for diagram chat.
packages/sdk/src/index.ts	Implements `diagramChat()` and helpers to parse the streamed response body.

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packages/sdk/src/types.ts

packages/sdk/src/index.ts

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

packages/sdk/src/index.ts:24

The PR description says the new DiagramChatRequest/DiagramChatResponse types are exposed for SDK consumers, but the entrypoint doesn’t re-export them. Since this package’s public surface is src/index.ts (and dist/index.d.ts), consider adding explicit export type { DiagramChatRequest, DiagramChatResponse } from './types.js' so consumers can import them from @mermaidchart/sdk without deep imports.

import type {
  AuthState,
  AuthorizationData,
  DiagramChatRequest,
  DiagramChatResponse,
  Document,
  InitParams,
  MCDocument,
  MCProject,
  MCUser,
  RepairDiagramRequest,
  RepairDiagramResponse,
  AICreditsUsage,
} from './types.js';
import { URLS } from './urls.js';

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packages/sdk/src/types.ts

packages/sdk/src/index.ts

Copilot · 2026-03-31T10:52:10Z

packages/sdk/src/index.test.ts

+      vi.spyOn(client, 'diagramChat').mockRejectedValue(
+        new AICreditsLimitExceededError('AI credits limit exceeded'),
+      );


This test doesn’t exercise the 402-handling logic in diagramChat() because it mocks client.diagramChat() itself to reject. Instead, mock the underlying axios .post() to reject with a { response: { status: 402, data: ... } } shape and assert that diagramChat() maps it to AICreditsLimitExceededError.

Suggested change

vi.spyOn(client, 'diagramChat').mockRejectedValue(

new AICreditsLimitExceededError('AI credits limit exceeded'),

);

// Mock the underlying axios call to simulate a 402 response from the API.

// eslint-disable-next-line @typescript-eslint/no-explicit-any

vi.spyOn((client as any).axios, 'post').mockRejectedValue({

response: {

status: 402,

data: {

message: 'AI credits limit exceeded',

},

},

});

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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Copilot · 2026-03-31T12:17:40Z

packages/sdk/src/index.ts

+      // can parse the Vercel AI SDK data-stream format after the request completes.
+      const response = await this.axios.post<string>(URLS.rest.openai.chat, requestBody, {
+        responseType: 'text',
+        timeout: 120_000,


diagramChat() hard-codes a 120s Axios timeout, which bypasses the instance-level requestTimeout configured via InitParams (and used when creating the Axios client). Consider respecting this.requestTimeout (or using something like max(this.requestTimeout, 120_000) and documenting it) so callers can control request timing consistently across SDK methods.

Suggested change

timeout: 120_000,

timeout: Math.max(this.requestTimeout ?? 0, 120_000),

Copilot · 2026-03-31T12:17:41Z

packages/sdk/src/index.ts

+    } catch (error: unknown) {
+      if (
+        error &&
+        typeof error === 'object' &&
+        'response' in error &&
+        error.response &&
+        typeof error.response === 'object' &&
+        'status' in error.response &&
+        (error as { response: { status: number } }).response.status === 402
+      ) {
+        const axiosError = error as { response: { status: number; data?: unknown } };
+        throw new AICreditsLimitExceededError(
+          typeof axiosError.response.data === 'string'
+            ? axiosError.response.data
+            : 'AI credits limit exceeded',
+        );
+      }


The 402->AICreditsLimitExceededError mapping logic is now duplicated in both repairDiagram() and diagramChat(). To reduce divergence risk (e.g., message formatting changes), consider extracting a small shared helper (or a private method) to detect the 402 Axios shape and build the error consistently.

added diagram chat functionality to sdk so mcp server can directly ch…

94c459b

…at with mermaid ai

Copilot AI review requested due to automatic review settings March 31, 2026 08:05

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Prashant-7718 added 2 commits March 31, 2026 15:18

fixed lint error

7578448

resolve comments and added test cases

7d76908

Copilot AI review requested due to automatic review settings March 31, 2026 10:48

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Prashant-7718 added 2 commits March 31, 2026 16:26

fixed lint error

a13e21c

updated test cases

908ecab

Prashant-7718 requested review from Copilot and sidharthv96 March 31, 2026 12:14

Prashant-7718 assigned aloisklink and unassigned aloisklink Mar 31, 2026

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AT-360 Added Diagram Chat Functionality To Mermaid/sdk So MCP Server Can Directly Access Mermaid AI #43

AT-360 Added Diagram Chat Functionality To Mermaid/sdk So MCP Server Can Directly Access Mermaid AI #43
Prashant-7718 wants to merge 5 commits intomainfrom
AT-360-new-mcp-tool-for-the-chat-with-mermaid

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-      vi.spyOn(client, 'diagramChat').mockRejectedValue(
-        new AICreditsLimitExceededError('AI credits limit exceeded'),
-      );
+      // Mock the underlying axios call to simulate a 402 response from the API.
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      vi.spyOn((client as any).axios, 'post').mockRejectedValue({
+        response: {
+          status: 402,
+          data: {
+            message: 'AI credits limit exceeded',
+          },
+        },
+      });

	timeout: 120_000,
	timeout: Math.max(this.requestTimeout ?? 0, 120_000),

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