mastra-ai/mastra · error · Error

System prompt is required for system prompt alignment…

Error message

System prompt is required for system prompt alignment scoring

What it means

In 'system' evaluation mode the prompt-alignment scorer grades the response against the combined system prompt. If getCombinedSystemPrompt(run.input) returns empty, there is no system prompt to judge against, so the scorer throws at run time.

Solutions

Ensure run.input contains a system-role message when using evaluationMode 'system'
Switch evaluationMode to 'user' if your runs have no system prompt
Verify getCombinedSystemPrompt's expected message format matches your run input structure

Example fix

// before
const scorer = createPromptAlignmentScorerLLM({ model, options: { evaluationMode: 'system' } });
await scorer.run({ input: { messages: [{ role: 'user', content: 'hi' }] }, output });
// after
const mode = hasSystemPrompt(runInput) ? 'system' : 'user';
const scorer = createPromptAlignmentScorerLLM({ model, options: { evaluationMode: mode } });

Defensive patterns

Strategy: validation

Validate before calling

if (evaluationMode === 'system' && !getCombinedSystemPrompt(run.input)) {
  throw new Error('Run has no system prompt; cannot score system-prompt alignment');
}

Type guard

function hasSystemPrompt(input) {
  return Boolean(getCombinedSystemPrompt(input));
}

Try / catch

try {
  const result = await scorer.run({ input, output });
} catch (e) {
  if (e.message.includes('System prompt is required')) {
    return { skipped: true, reason: 'run has no system prompt' };
  }
  throw e;
}

Prevention

Only select mode 'system' for conversations that actually carry a system message
Keep system instructions in a system-role message, not the first user message
Derive evaluationMode from the run's content instead of hardcoding it

When it happens

Trigger: Running the scorer with evaluationMode = 'system' on a run whose input contains no system-role messages — e.g. a plain user/assistant exchange scored with the wrong mode.

Common situations: Selecting mode 'system' in config while the scored conversations have no system message; system instructions embedded in the first user message instead of a system role; misconfigured extractor that ignores the system role.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/81bc015f7f58e459. Report an issue: GitHub.

Appendix: source

Thrown at packages/evals/src/scorers/llm/prompt-alignment/index.ts:123

    judge: {
      model,
      instructions: PROMPT_ALIGNMENT_INSTRUCTIONS,
    },
  })
    .analyze({
      description: 'Analyze prompt-response alignment across multiple dimensions',
      outputSchema: analyzeOutputSchema,
      createPrompt: ({ run }) => {
        const userPrompt = getUserMessageFromRunInput(run.input) ?? '';
        const systemPrompt = getCombinedSystemPrompt(run.input) ?? '';
        const agentResponse = getAssistantMessageFromRunOutput(run.output) ?? '';

        // Validation based on evaluation mode
        if (evaluationMode === 'user' && !userPrompt) {
          throw new Error('User prompt is required for user prompt alignment scoring');
        }
        if (evaluationMode === 'system' && !systemPrompt) {
          throw new Error('System prompt is required for system prompt alignment scoring');
        }
        if (evaluationMode === 'both' && !userPrompt && !systemPrompt) {
          throw new Error('A user or system prompt is required for combined alignment scoring');
        }
        if (!agentResponse) {
          throw new Error('Agent response is required for prompt alignment scoring');
        }

        return createAnalyzePrompt({
          userPrompt,
          systemPrompt,
          agentResponse,
          evaluationMode,
          conversationHistory: historyOptions && getConversationHistoryFromRunInput(run.input, historyOptions),
        });
      },
    })
    .generateScore(({ results }) => {

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