Skip to main content
XMLDir

XML error · InvalidTag

Tag is an invalid name

An element name breaks XML's naming rules — usually because it starts with a digit.

Tag '2026-total' is an invalid name.

What it means

XML names must begin with a letter or underscore and may then contain letters, digits, hyphens, underscores and periods. A leading digit, a space, or most punctuation is invalid.

This is the classic failure of generating XML element names from data — column headers, JSON keys, or year labels become element names that XML will not accept.

What usually causes it

  • Element names generated from data: <2026-total>, <1st-quarter>.
  • A space or slash in a generated name.
  • Names starting with the reserved sequence xml (in any case).
  • A name containing a character that is legal in JSON keys but not in XML names.

How to fix it

  • Prefix generated names so they start with a letter or underscore: <y2026-total>.
  • Replace illegal characters with hyphens or underscores when mapping data to names.
  • Better still, put the variable part in an attribute and keep the element name fixed: <total period="2026"/>.

The same error elsewhere

Different parsers, same defect. If you arrived with one of these messages, you are in the right place.

  • libxml2 (PHP, lxml, Nokogiri)

    StartTag: invalid element name

  • Xerces (Java)

    Element type "2026-total" must be followed by either attribute specifications, ">" or "/>".

  • expat (Python)

    not well-formed (invalid token): line 2, column 3

  • .NET System.Xml

    Name cannot begin with the '2' character.

Before and after

Both snippets are checked on every build: the first is confirmed to produce the error above, the second to parse cleanly.

Fails
<report>
  <2026-total>1200</2026-total>
</report>
Parses
<report>
  <total period="2026">1200</total>
</report>
Check your document← All XML errors

Where this bites most

Other XML errors

Get started

Bring order to the XML your team can't afford to ignore.

Create a free account and get a private workspace to search, validate, diff, and monitor your XML feeds, sitemaps, schemas, and vendor integrations.

Get started freeSign in