XSLT Tester Online

Why an XSLT result is rarely what you expected

XSLT is declarative. You do not write the order things happen in, the processor decides which template handles which node. When the output is wrong, the question is therefore seldom "what is on this line" but "did this line run at all, and for which nodes". These are the usual causes.

The namespace that makes nothing match

By far the most common one. If the XML declares a default namespace, its elements are in that namespace, and a path without a prefix does not find them.

<Order xmlns="urn:example:orders">
  <OrderNumber>SO-10482</OrderNumber>
</Order>

<!-- Matches nothing: looks for Order in no namespace -->
<xsl:template match="Order">

<!-- XSLT 1.0: declare a prefix and use it -->
<xsl:template match="o:Order" xmlns:o="urn:example:orders">

<!-- XSLT 2.0 and later: set it once on xsl:stylesheet -->
<xsl:stylesheet version="3.0" xpath-default-namespace="urn:example:orders" ...>

Text that appears from nowhere

Nodes that no template matches are handled by the built-in rules, which walk down the tree and copy every text node to the output. Stray values between your elements mean that something was not matched. An empty template for the parts you do not want, or a more specific xsl:apply-templates select, removes them.

The context changed

Inside xsl:for-each and inside a template, paths are relative to the current node. Quantity works inside a loop over Line and returns nothing one level up. A variable declared before the loop is the usual way to bring an outer value in.

The wrong version of XSLT

Browsers have only ever had XSLT 1.0 built in, and many online testers are limited to it as well. xsl:for-each-group, regular expressions, date functions, sequences and user-defined functions need 2.0 or later. A stylesheet written for Saxon on a server fails in a 1.0 processor with an error that seldom says "wrong version".

How to find the cause faster

The classic method is to add xsl:message in a few places and run again. In Nodeflip you select the lines you wonder about instead. A panel shows what exactly those lines write for the file you chose: elements, attributes and text, once for every time the lines run. No output means the lines never ran, which points at the match or the context. Select a variable to see its value.