initial, seems to work

.gitignore

@@ -373,3 +373,5 @@ FodyWeavers.xsd
 # Local History for Visual Studio Code
 .history/
 
+MagicCompRules.txt
+MagicCompRules.NoNums.txt

.vscode/launch.json

@@ -0,0 +1,26 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            // Use IntelliSense to find out which attributes exist for C# debugging
+            // Use hover for the description of the existing attributes
+            // For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
+            "name": ".NET Core Launch (console)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            // If you have changed target frameworks, make sure to update the program path.
+            "program": "${workspaceFolder}/bin/Debug/net5.0/mtg-rules-dler.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}",
+            // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
+            "console": "internalConsole",
+            "stopAtEntry": false
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach"
+        }
+    ]
+}

.vscode/tasks.json

@@ -0,0 +1,42 @@
+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/mtg-rules-dler.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/mtg-rules-dler.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "${workspaceFolder}/mtg-rules-dler.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        }
+    ]
+}

Program.cs

@@ -0,0 +1,64 @@
+using System;
+using System.IO;
+using System.Net;
+using System.Text.RegularExpressions;
+using HtmlAgilityPack;
+
+namespace mtg_rules_dler
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+
+            HtmlWeb web = new HtmlWeb();
+
+            var htmlDoc = web.Load("https://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules");
+
+            var links = htmlDoc.DocumentNode.SelectNodes("//div[contains(@id,'comprehensive-rules')]//a");
+            if (links == null || links.Count == 0)
+            {
+                Console.Error.WriteLine("can't find any links.");
+                return;
+            }
+
+            var linkTarget = "";
+            var found = false;
+            foreach (var link in links)
+            {
+                linkTarget = link.Attributes["href"]?.Value;
+                if (linkTarget?.EndsWith(".txt") == true)
+                {
+                    found = true;
+                    break;
+                }
+            }
+            if (!found)
+            {
+                Console.Error.WriteLine("couldn't find link to rules.txt");
+                return;
+            }
+
+            var request = WebRequest.Create(linkTarget);
+            var response = request.GetResponse();
+
+            var responseAsText = "";
+            using (var dataStream = new StreamReader(response.GetResponseStream()))
+            {
+                responseAsText = dataStream.ReadToEnd();
+            }
+
+            if (File.Exists("MagicCompRules.txt"))
+            {
+                if (File.ReadAllText("MagicCompRules.txt") == responseAsText)
+                {
+                    Console.WriteLine("no update.");
+                    return;
+                }
+            }
+            File.WriteAllText("MagicCompRules.txt", responseAsText);
+
+            File.WriteAllText("MagicCompRules.NoNums.txt", new Regex("\\b\\d+(\\.\\d+)?([\\w]+)?\\b").Replace(responseAsText, "#"));
+        }
+    }
+}

mtg-rules-dler.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+    <RootNamespace>mtg_rules_dler</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="HtmlAgilityPack" Version="1.11.39" />
+  </ItemGroup>
+
+</Project>