What causes a duplicate unique property error in structured data?

Definition: A duplicate unique property error appears when a JSON-LD object supplies two definitions for one property that Google expects to occur once in that object. Google's Unparsable structured data report gives two @context values as its example; the issue is in the JSON-LD object's structure.

Key facts

• Google's Unparsable structured data report describes this error as two definitions for a unique property, with two @context values as the example.
• RFC 8259 says that names within a JSON object should be unique and that duplicate names can produce unpredictable behavior.
• The JSON-LD 1.1 specification states that names in a JSON-LD object must be unique.
• Google's general structured data guidelines list JSON-LD as a supported format and mark it as recommended.

Why does the error occur?

JSON-LD uses JSON objects made of name and value pairs. RFC 8259 states, “The names within an object SHOULD be unique.” It also says that when names are not unique, software may keep only the last pair, report an error, fail to parse the object, or report all pairs including duplicates.

The W3C JSON-LD 1.1 specification applies the stronger rule that names in a JSON-LD object must be unique. In the same specification, @context is the keyword used to define the short-hand names used throughout a JSON-LD document. Google's example therefore points to a repeated object member such as this:

{
  "@context": "https://schema.org/",
  "@type": "Recipe",
  "@context": "https://schema.org"
}

The two @context members are two definitions of one property in the same object. The JSON-LD specification says that a context is introduced with an entry whose key is @context. It also says that multiple contexts may be combined in an array processed in order, which keeps one @context member in the object.

What does Google report?

Google's Unparsable structured data report lists structured data that could not be parsed because of a serious syntax error, so the intended type, such as Job or Event, could not be determined. The report is available for a property only when Google found unparseable structured data on the site. Google classifies every item in this report as a critical structured data error, with no warnings or valid items.

The report sorts errors by severity using the number of affected pages and other factors. Google also documents that one error affecting multiple pages commonly comes from an underlying template error. An issue can affect items on different pages or multiple items on one page. Selecting an error row shows affected pages, error details, and debugging links.

How should you repair and check the markup?

Remove the repeated member from the affected JSON-LD object and keep one @context definition. A minimal object with one context member follows the structure in Google's structured data introduction:

{
  "@context": "https://schema.org/",
  "@type": "Recipe",
  "name": "Non-Alcoholic Piña Colada"
}

Google's report help recommends starting from an empty object and adding the broken code back piece by piece when the error is hard to locate. After the issue is fixed, it says to click Validate Fix in the error details page. Google's general guidelines identify the Rich Results Test and URL Inspection tool as the tools for testing technical compliance, and say that they catch most technical errors.

Related terms

• JSON-LD
• Structured data
• Schema.org @id

FAQ

Is this the same as putting several structured data items on one page?

Google documents multiple items on a page as a supported pattern. They can be nested or specified as individual items. The duplicate unique property error concerns two definitions inside one object.

Can multiple contexts be used in JSON-LD?

Yes. The JSON-LD specification says that multiple contexts may be combined using an array, processed in order. That array is the value of one @context member; the error concerns repeated definitions of the member.

Where can you see which pages are affected?

Select the error row in the Unparsable structured data report. Google says the resulting details show affected pages, error details, and links for debugging tools. The Rich Results Test can then test the repaired syntax.

Sources

1. Google Search Console Help, "Unparsable structured data report", undated
2. Google Search Central, "General structured data guidelines", 10 July 2026
3. Google Search Central, "Introduction to structured data markup in Google Search", 10 December 2025
4. IETF, "The JavaScript Object Notation (JSON) Data Interchange Format", December 2017
5. W3C, "JSON-LD 1.1", 16 July 2020

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