mastra-ai/mastra · error · Error

Extractor "${extractor.slug}" output did not match its schem

Error message

Extractor "${extractor.slug}" output did not match its schema: ${failures[0] ?? 'invalid value'}

What it means

`parseExtractorValue` validates the raw text extracted from an output tag against the extractor's Zod schema, trying JSON.parse first and then the plain string as candidates. If no candidate passes `schema.safeParse`, the library throws with the first Zod failure message. The result is captured in parseExtractedValues as a per-slug failure, but this underlying throw surfaces when the model output doesn't conform to the declared schema.

Source

Thrown at packages/memory/src/processors/observational-memory/extractor.ts:276

      add(JSON.parse(trimmed));
    } catch {
      // Plain strings are valid extractor values.
    }
  }

  return candidates;
}

export function parseExtractorValue<T>(extractor: Extractor<T>, raw: string): T {
  const failures: string[] = [];
  for (const candidate of candidateValues(raw)) {
    const parsed = extractor.schema.safeParse(candidate);
    if (parsed.success) {
      return parsed.data;
    }
    failures.push(parsed.error.message);
  }
  throw new Error(`Extractor "${extractor.slug}" output did not match its schema: ${failures[0] ?? 'invalid value'}`);
}

export interface ParsedExtractedValues {
  values: Record<string, unknown>;
  failures: Array<{ slug: string; error: string }>;
}

function parseExtractedValuesObject(raw: string): Record<string, unknown> | undefined {
  const trimmed = raw.trim();
  if (!trimmed || trimmed.startsWith('Write only the extracted values JSON object here.')) {
    return undefined;
  }

  const parsed = JSON.parse(trimmed) as unknown;
  if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
    throw new Error(`${EXTRACTED_VALUES_TAG} must contain a JSON object.`);
  }
  return parsed as Record<string, unknown>;

View on GitHub (pinned to 75dd419e61)

Solutions

1. Loosen or correct the Zod schema so valid model outputs parse (add coercion, .catch(), optional fields, .default()).
2. Sharpen the extractor `instructions` to specify the exact output format (e.g. 'Return only a JSON object with fields X and Y').
3. Use a more capable model for the observer/reflector if it repeatedly fails to produce valid JSON.
4. Handle the failure gracefully via parseExtractedValues' returned `failures` array rather than letting the throw propagate, and retry the extraction.

Example fix

// before
schema: z.object({ count: z.number() }) // model returns "{\"count\": \"3\"}"
// after
schema: z.object({ count: z.coerce.number() })

const preview = extractRawTag(output, slug);
const result = schema.safeParse(preview);
if (!result.success) logger.warn('Extractor output will fail schema', { slug, issues: result.error.issues });

function matchesSchema(value, schema) { return schema.safeParse(value).success; }

const { values, failures } = parseExtractedValues(output, extractors);
for (const f of failures) {
  if (f.error.includes('did not match its schema')) {
    logger.warn('Schema mismatch, will retry extraction', { slug: f.slug });
  }
}

When it happens

Trigger: Structured extractor's schema expects a number/object but the model emitted prose; JSON in the tag is valid JSON but wrong shape (missing fields, string instead of number); the model wrapped the value in markdown fences or extra text inside the tag; inline `<slug>` tag content that is a plain string but schema requires an object.

Common situations: Small/weak models ignoring JSON formatting instructions; schema too strict (e.g. .url(), enum, min length) for what the model produces; changing a schema after deployment while persisted/old outputs use the old shape; nested quotes breaking JSON.parse.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• OBSERVABILITY_INVALID_CONFIG
• OBSERVABILITY_INVALID_INSTANCE_CONFIG
• Invalid structured content for tool ${request.params.name}:
• ${EXTRACTED_VALUES_TAG} must contain a JSON object.
• Observer produced degenerate output after retry. ${describeD

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/5482dfa5a6f58241. Report an issue: GitHub.