What kinds of errors can it introduce?

One of: removing a closing tag, unescaping a literal & character, removing quotes from an attribute value, mismatching a closing tag's name, or leaving an element unclosed. One is picked at random each time.

Does it always succeed?

It requires well-formed input to start with (since "breaking" invalid XML doesn't make sense) and needs at least one applicable location for the chosen mutation; very small or attribute-free documents may not have every mutation type available.

Does it tell me what it broke?

Yes, the specific mutation applied (e.g. "Mismatched a closing tag") is shown alongside the result, so you know what kind of error the output demonstrates.

Why would I want deliberately broken XML?

It's useful for testing that a parser or validator correctly rejects malformed input, building a suite of negative test cases, or demonstrating a specific class of XML error for documentation or teaching purposes.

XML Error Injector - Generate Broken XML Test Fixtures Online

Overview

Introduction

Testing that a parser correctly rejects bad input means having bad input to test with.

This tool generates it on demand from a valid starting document.

What Is XML Error Injector?

A test-fixture generator that applies one random well-formedness-breaking mutation to otherwise-valid XML.

The mutation is chosen from a small set of realistic error patterns.

How XML Error Injector Works

The input is first validated (it must be well-formed to start).

A set of mutation strategies is tried in random order until one actually changes the input, each strategy targets a specific class of error (unclosed tags, mismatched tags, unescaped entities, unquoted attributes).

When To Use XML Error Injector

Use it to build negative test cases for a parser or validator.

It's also useful for demonstrating what a specific kind of XML error looks like.

Often used alongside XML Validator and XML Prettifier.

Features

Advantages

Generates realistic, specific error patterns rather than random text corruption.
Tells you exactly what kind of error was introduced.
Runs entirely client-side.

Limitations

Requires well-formed input to start.
The mutation applied is random each time, run it multiple times if you need a specific error type.

Examples

Mismatching a closing tag

Input

<a><b>x</b></a>

Output

<a><b>x</b></corrupted>

One of the closing tags was renamed to </corrupted>, producing a mismatched-tag error.

Best Practices & Notes

Best Practices

Run this multiple times if you need to test several different error types, one call applies exactly one mutation.
Use the XML Validator afterward to confirm the output actually fails validation the way you expect.
Save a few generated variants as a small negative-test-case suite rather than regenerating on every test run.

Developer Notes

Mutation strategies are tried in shuffled order until one produces a change, so the same input can produce different error types across runs rather than always favoring one strategy.

XML Error Injector Use Cases

Building negative test cases for an XML parser or validator
Demonstrating a specific class of XML syntax error
Fuzz-testing error handling in an XML ingestion pipeline

Common Mistakes

Expecting this to work on already-invalid XML, input must be well-formed first.
Assuming the same mutation type is applied every time, it's chosen randomly on each run.

Tips

Use the XML Validator afterward to confirm the output actually fails validation the way you expect.
Check the FAQ above if the output doesn't look like what you expected.

XML Error Injector