mastra-ai/mastra · error · Error

Could not generate title from input ${JSON.stringify(message

Error message

Could not generate title from input ${JSON.stringify(message)}

What it means

The agent's internal title generation normalizes the provided `message` through MessageList and needs at least one user message to format a prompt for the title model. If the normalized message list is empty (no last message), it throws this plain Error with the JSON-serialized input. This is an input-shape problem, not a model failure.

Source

Thrown at packages/core/src/agent/agent.ts:3658

    const observabilityContext = resolveObservabilityContext(rest);
    // need to use text, not object output or it will error for models that don't support structured output (eg Deepseek R1)
    const llm = await this.getLLM({ requestContext, model });
    // Register Mastra on the LLM (if any) so the inner agentic loop has access
    // for storage/observability. Idempotent.
    if (this.#mastra) {
      llm.__registerMastra(this.#mastra);
    }

    let userContent: string;

    if (messages && messages.length > 0) {
      // Multi-message path: format all messages with roles
      userContent = this.formatMessagesForTitle(messages);
    } else if (message) {
      // Single message path (backward compat): normalize and format
      const normMessage = new MessageList().add(message, 'user').get.all.aiV5.ui().at(-1);
      if (!normMessage) {
        throw new Error(`Could not generate title from input ${JSON.stringify(message)}`);
      }
      userContent = this.formatMessagesForTitle([normMessage]);
    } else {
      throw new Error('Either message or messages must be provided');
    }

    if (!userContent) {
      return undefined;
    }

    // Resolve instructions using the dedicated method
    const systemInstructions = await this.resolveTitleInstructions(requestContext, instructions);

    let text = '';

    if (isSupportedLanguageModel(llm.getModel())) {
      const messageList = new MessageList()
        .add(

View on GitHub (pinned to 75dd419e61)

Solutions

Check the input for emptiness before calling title generation and skip the call (or supply a placeholder) when there is no user content.
Pass a plain non-empty string instead of a pre-built message object if the shape is uncertain.
If generating titles from multiple messages, use the `messages` array path with at least one populated user message.

Example fix

// before
await agent.generateTitle({ message: userInput }); // userInput may be ''
// after
if (userInput && userInput.trim()) {
  await agent.generateTitle({ message: userInput });
}

Defensive patterns

Strategy: validation

Validate before calling

function hasTitleableContent(input: unknown): boolean {
  if (typeof input === 'string') return input.trim().length > 0;
  if (Array.isArray(input)) return input.length > 0;
  if (input && typeof input === 'object') {
    const parts = (input as any).content?.parts ?? (input as any).parts;
    return Array.isArray(parts) ? parts.length > 0 : Object.keys(input as object).length > 0;
  }
  return false;
}

Type guard

function isNonEmptyUserMessage(m: unknown): m is { role: 'user'; content: string } {
  const msg = m as any;
  return !!msg && msg.role === 'user' && (typeof msg.content === 'string' ? msg.content.trim().length > 0 : !!msg.content?.parts?.length);
}

Try / catch

try {
  await agent.generateTitle({ message });
} catch (err) {
  if ((err as Error).message.startsWith('Could not generate title from input')) {
    return null; // nothing titleable — skip title generation gracefully
  }
  throw err;
}

Prevention

Gate title generation on non-empty, trimmed user input.
Pass plain strings rather than hand-built message objects when unsure of the shape.
Treat title generation as best-effort: catch and fall back to a default thread title.

When it happens

Trigger: Calling the title-generation path (e.g. agent.generateTitle / memory title generation) with a `message` whose content normalizes to zero messages — an empty string, an empty array of parts, or a malformed message object with no usable content.

Common situations: Auto-generating memory thread titles from empty user input, passing a message object that was never populated, or piping a UI value (empty input box) directly into title generation.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/ec4a9d6d48043f2a. Report an issue: GitHub.