HTML / XML / JS, low-level validity (cross-cutting)LowInferred
BOM/invisible characters
A byte-order mark or stray invisible characters at the start of a file can disrupt parsing, push output before the head, or break scripts. Files should be clean UTF-8 without a BOM.
What it is
Hidden characters corrupt markup.
Why it matters
Can break parsing/JSON-LD.
How to fix it
Strip BOM/invisibles.
How to find it on your site
- Check source files for a BOM or invisible characters, especially at the start.
- Re-save files as UTF-8 without BOM.
- Strip stray zero-width or control characters.
- Re-validate the document.
Cross-reference to ranking and citation factors
A BOM or invisible characters can corrupt parsing and output. Clean encoding keeps the document well-formed.
Impact
Low. Inferred.
Evidence
Clean markup parses reliably. Google Search Central, Structured data general guidelines