ADMXComparer – Take Control of Administrative Template Changes from the Command Line

Group Policy Administrative Templates (ADMX/ADML) are constantly evolving. Every new Windows release, browser version, or feature update introduces changes—new settings, removed settings, or sometimes even a reorganization of templates.

But answering simple questions like:

What exactly changed between two ADMX versions?
Which policies are new or removed?
Did Microsoft move a policy to a different ADMX file?

…is surprisingly difficult with standard tools.

This is exactly where ADMXComparer comes in.

🔎 What is ADMXComparer?

ADMXComparer is a C# console tool built on .NET Framework 4.8.1 that compares two sets of Administrative Templates (ADMX) together with their language files (ADML) and generates a single, structured HTML report with all differences.

Key capabilities include:

Comparing which ADMX files exist in one set but not the other
Comparing policy settings inside each ADMX file
Resolving policy display names from ADML files (if available)
Detecting settings that were moved between ADMX files
Showing GPO path and registry key details per setting
Producing a single combined HTML report with drill-down details

All results are presented in one clean, shareable HTML report.

⚠️ The Problem with Traditional ADMX Comparisons

If you’ve ever tried to compare Administrative Templates manually, you already know the challenges:

ADMX files reference strings stored in ADML files
Policies are organized in nested category structures
The same setting can exist in different ADMX files across versions
Internal policy names differ from display names
Registry keys are not obvious from a simple file diff

A simple file comparison tool cannot provide meaningful insight.

ADMXComparer solves this by understanding the structure and semantics of ADMX/ADML files—not just their raw content. ADMXComparer_Blog_Input

🧠 Typical Use Cases

ADMXComparer is designed for administrators, consultants, and IT professionals who need to understand template changes quickly.

🪟 Compare Windows Administrative Templates

Example:

Windows 10 22H2 vs. Windows 11 24H2

🌐 Compare Browser Templates

Example:

Microsoft Edge ADMX version 143 vs. 145

🔄 Change Analysis

Which policies are new?
Which policies were removed?
Which policies were moved?

📝 Documentation & Release Notes

The HTML report can be used directly as:

Internal documentation
Customer reports
Blog content
Change tracking artifacts

⚙️ How ADMXComparer Works

The tool compares two template sets, each consisting of:

ADMX files (mandatory)
ADML language files (optional, auto-detected if not provided)
A display name (optional, defaults applied if omitted)

🔍 What the tool analyzes

ADMXComparer extracts and compares:

ADMX file names
Policy definitions
Display names (resolved via ADML where possible)
Category hierarchy (GPO path)
Registry keys
Policy class (User / Machine / Both)
Cross-ADMX policy presence to detect moved settings

It also dynamically resolves XML namespaces per file, ensuring compatibility with vendor templates such as Microsoft Edge.

💻 Command-Line Usage

ADMXComparer is designed as a simple but powerful command-line tool.

📌 Mandatory parameters

-ADMXPath1 -ADMXPath2

🧩 Optional parameters

-ADMLPath1 -ADMLPath2
-SetName1 -SetName2
-Lang or -Language
-Output
-?

🧠 ADML resolution logic (simplified)

If no ADML path is specified, the tool will:

Use -Lang (for example en-US) to locate a subfolder
Otherwise try en-us automatically
Fall back to internal policy names if no ADML files are found

This behavior is documented directly in the report header.

▶️ Example: Windows 10 vs. Windows 11 (auto language detection)

ADMXComparer.exe -ADMXPath1 "C:\Templates\Windows10" -ADMXPath2 "C:\Templates\Windows11" -Lang "en-US" -SetName1 "Windows 10 22H2" -SetName2 "Windows 11 24H2"

🌐 Example: Microsoft Edge comparison with explicit ADML paths

ADMXComparer.exe -ADMXPath1 "C:\Templates\Edge143" -ADMLPath1 "C:\Templates\Edge143\en-US" -SetName1 "Edge 143" -ADMXPath2 "C:\Templates\Edge145" -ADMLPath2 "C:\Templates\Edge145\en-US" -SetName2 "Edge 145" -Output "C:\Reports\Edge143_vs_Edge145.html"

🌍 Example: Minimal comparison (auto fallback behavior)

ADMXComparer.exe -ADMXPath1 "C:\Templates\SetA" -ADMXPath2 "C:\Templates\SetB"

📊 The HTML Report – What You Get

The output is a single HTML file automatically opened in your default browser.

Default filename:

ADMXCompareReport_<timestamp>.html

🧭 Report header (new)

At the top of the report you now get a metadata header block including:

Report title
Creation timestamp
Tool version and author
Exact command-line parameters used
ADML / language fallback resolution notes
Jump links to main report sections

📈 Report Sections

1. Overview / Summary

Number of ADMX files per set
File differences
Setting differences

2. ADMX Files Only in One Set

Quick overview of newly added or removed templates.

3. Policy Differences per ADMX File

Settings that exist only in one version within a specific ADMX.

4. Complete List of Unmatched Policies

Compact table showing only:

ADMX
Policy Name

5. Settings Comparison (cross-ADMX)

This is the most powerful section:

Detects moved settings
Shows ADMX assignment per set
Click to expand full details

Each setting includes:

Class (User / Machine / both combined)
GPO path
Registry key
ADMX assignment in both sets

🧭 How to Interpret the Results

🔹 “Only in <SetName>”

The file or setting exists only in one set.

🔹 “Moved”

The same policy exists in both sets but was assigned to a different ADMX file.

🔹 Fallback display names

If ADML is missing or incomplete, internal policy names are shown instead.

The report header will indicate if fallback resolution was used.

🔹 Vendor ADMX compatibility

A previous limitation with XML namespaces (e.g., Edge ADMX) has been resolved — differences are now correctly detected.

💡 Why This Tool is Useful

ADMXComparer provides several key advantages:

Compares both ADMX files and policy content
Detects moved settings (not just added/removed)
Resolves ADML display names correctly
Shows GPO path and registry key for each setting
Supports automatic ADML language detection
Produces a single clean HTML report with navigation

It is particularly useful for:

Enterprise administrators
GPO consultants
Security baseline comparisons
Change management and release documentation

🛠️ Technical Details

Language: C#
Framework: .NET Framework 4.8.1
Type: Console application
Output: Single HTML report
XML parsing of ADMX/ADML
Dynamic XML namespace handling (Windows + vendor templates)
Automatic browser launch

⚠️ Known Limitations

Missing ADML files lead to fallback display names
Large template sets can produce large HTML files
“Moved” detection is based on internal policy names
The tool focuses on added/removed/moved settings (not every internal attribute change)

🚀 Final Thoughts

Keeping track of changes in Administrative Templates is essential—but traditionally difficult.

ADMXComparer makes this process transparent, structured, and easy to understand.