mastra-ai/mastra · error · HTTPException

Editor is not configured

Error message

Editor is not configured

What it means

A stored-agents route calls mastra.getEditor() and throws a 500 HTTPException when no editor is configured on the Mastra instance. The editor powers prompt preview/build functionality for stored agents; like storage, it is optional and must be explicitly registered. Without it the preview endpoint cannot run.

Source

Thrown at packages/server/src/server/handlers/stored-agents.ts:1179

/**
 * POST /stored/agents/preview-instructions - Preview resolved instructions
 */
export const PREVIEW_INSTRUCTIONS_ROUTE = createRoute({
  method: 'POST',
  path: '/stored/agents/preview-instructions',
  responseType: 'json',
  bodySchema: previewInstructionsBodySchema,
  responseSchema: previewInstructionsResponseSchema,
  summary: 'Preview resolved instructions',
  description:
    'Resolves an array of instruction blocks against a request context, evaluating rules, fetching prompt block references, and rendering template variables. Returns the final concatenated instruction string.',
  tags: ['Stored Agents'],
  requiresAuth: true,
  handler: async ({ mastra, blocks, context }) => {
    try {
      const editor = mastra.getEditor();
      if (!editor) {
        throw new HTTPException(500, { message: 'Editor is not configured' });
      }

      const result = await editor.prompt.preview(blocks, context ?? {});

      return { result };
    } catch (error) {
      return handleError(error, 'Error previewing instructions');
    }
  },
});

View on GitHub (pinned to 75dd419e61)

Solutions

1. Configure the editor on your Mastra instance, e.g. new Mastra({ ..., editor: new Editor(...) }) per the agent-builder setup docs.
2. Confirm the editor package is installed and imported in the server entrypoint.
3. Check environment gating so the editor is registered in the environment where previews are used.
4. If the editor is intentionally absent, hide/disable prompt-preview UI paths.

Example fix

// before
new Mastra({ agents, storage });

// after
import { Editor } from '@mastra/editor';
new Mastra({ agents, storage, editor: new Editor() });

const editor = mastra.getEditor();
if (!editor) throw new Error('Editor is not configured; prompt preview is unavailable.');

function hasEditor(m: Mastra): boolean {
  return typeof m.getEditor === 'function' && !!m.getEditor();
}

try {
  const preview = await client.previewAgentPrompt(blocks, ctx);
} catch (e) {
  if (isMastraServerError(e) && e.status === 500 && e.message.includes('Editor is not configured')) {
    // disable preview UI / show setup guidance
  } else throw e;
}

When it happens

Trigger: POSTing to the editor prompt-preview route (blocks + context body) on a Mastra server whose instance has no editor set, so mastra.getEditor() returns undefined.

Common situations: Using the Studio/agent-builder prompt preview before configuring the editor; the editor only wired in certain environments; forgetting the editor option when migrating from a non-editor setup.

Related errors

• AcpAgent does not support resuming suspended generate calls
• ACP prompt stopped before completing: ${response.stopReason}
• server.drainTimeout must be a finite number between 0 and 21
• Agents storage domain is not available
• Mastra instance is required for conversations

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/07ec3c55d9b51050. Report an issue: GitHub.