mastra-ai/mastra · error · Error

Extractor slug "${slug}" is reserved by Observational Memory

Error message

Extractor slug "${slug}" is reserved by Observational Memory.

What it means

Extractor names are slugified into kebab-case and used as XML tags in prompts and metadata keys. Observational Memory reserves a set of tags for its own protocol (`observations`, `observation`, `extracted-values`, `thread`, `message`, `messages`, `conversation`, `history`, `system`, `user`, `assistant`, `tool`, plus built-in extractor slugs like `thread-title`) and refuses user extractors whose slug collides, to avoid corrupting the prompt/output parsing.

Source

Thrown at packages/memory/src/processors/observational-memory/extractor.ts:162

    if (!name) {
      throw new Error('Extractor name is required.');
    }
    if (!isHook && !config.instructions) {
      throw new Error(`Extractor "${name}" must include instructions.`);
    }
    if (instructions !== undefined && !instructions) {
      throw new Error(`Extractor "${name}" must include instructions.`);
    }
    if (isHook && !config.onExtracted) {
      throw new Error(`Hook extractor "${name}" must include an onExtracted handler.`);
    }
    if (isHook && (config.instructions || config.schema)) {
      throw new Error(`Hook extractor "${name}" cannot include instructions or a schema.`);
    }
    assertValidSlug(slug, name);
    if (!internal && RESERVED_XML_TAGS.has(slug)) {
      throw new Error(`Extractor slug "${slug}" is reserved by Observational Memory.`);
    }

    this.name = name;
    this.slug = slug;
    this.instructionsConfig = config.instructions ?? '';
    this.schemaConfig = config.schema;
    this.instructions = instructions ?? '';
    this.schema = (
      isHook ? z.unknown() : typeof config.schema === 'function' ? z.string() : (config.schema ?? z.string())
    ) as z.ZodType<T>;
    this.mode = isHook ? 'hook' : internal || !config.schema ? 'inline' : 'structured';
    this.includePreviousExtraction = isHook ? false : (config.includePreviousExtraction ?? true);
    this.metadataKeyPath = isHook ? false : (config.metadataKeyPath ?? `extracted.${slug}`);
    this.onExtracted = config.onExtracted;
    this.retryStructuredExtractionOnEmptyObject = config.retryStructuredExtractionOnEmptyObject ?? false;
    this.internal = internal;
  }

View on GitHub (pinned to 75dd419e61)

Solutions

1. Rename the extractor so its kebab-case slug does not match a reserved tag (e.g. 'Observations' → 'key-observations').
2. Avoid built-in extractor slugs: current-task, suggested-response, thread-title.
3. Check the slug with slugifyExtractorName(name) before constructing.

Example fix

// before
new Extractor({ name: 'Thread Title', instructions: '...' });
// after
new Extractor({ name: 'Session Title', instructions: '...' });

const RESERVED = new Set(['observations','observation','extracted-values','thread','message','messages','conversation','history','system','user','assistant','tool','current-task','suggested-response','thread-title']);
const slug = slugifyExtractorName(name);
if (RESERVED.has(slug)) throw new Error(`Name "${name}" collides with reserved slug "${slug}"`);

function isSafeExtractorName(name) {
  return !RESERVED.has(slugifyExtractorName(name));
}

try {
  const extractor = new Extractor({ name, instructions });
} catch (e) {
  if (e.message.includes('is reserved by Observational Memory')) {
    logger.error('Reserved extractor slug', { name });
  } else { throw e; }
}

When it happens

Trigger: Naming an extractor 'Observations', 'Thread Title', 'User', 'System', 'Extracted Values', etc. — any name whose slugified form matches a reserved tag; e.g. name: 'USER' or 'my observations' → slug 'observations'? no ('my-observations' ok), but name 'Observations!' slugifies to 'observations' and throws.

Common situations: Trying to override built-in extractors (current-task, suggested-response, thread-title) by reusing their names; naming extractors after protocol tags; generic names like 'History' or 'Messages' that collide.

Related errors

• Extractor slug "${extractor.slug}" is reserved by Observatio
• Extractor name "${name}" must produce a non-empty slug.
• Extractor name "${name}" produced invalid slug "${slug}".
• Extractor name is required.
• Duplicate extractor slug "${extractor.slug}" from "${previou

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/0b8557401792e17a. Report an issue: GitHub.