diff --git a/content_filter.go b/content_filter.go
index 9915b74..59a4dca 100644
--- a/content_filter.go
+++ b/content_filter.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -522,15 +523,23 @@ func (f *ContentFilter) evaluateRule(rule FilterRule, app AppInfo, effectiveRati
 		case "eq":
 			return app.Category == rule.Value
 		case "contains":
-			return app.Category == rule.Value
+			return strings.Contains(app.Category, rule.Value)
 		}
 
 	case "author":
 		switch rule.Operator {
 		case "eq":
-			return app.Author == rule.Value
+			// Addresses have two renderings of one key: a contract always stores the
+			// dero1 form (ADDRESS_STRING leaves Mainnet true so consensus cannot depend
+			// on the node's network), while a wallet on a simulator shows deto1. They are
+			// bech32, so prefix AND checksum differ and a string compare reads one wallet
+			// as two. Compare the decoded keys, as UpdateINDEX does.
+			return sameINDEXAuthor(app.Author, rule.Value)
 		case "contains":
-			return app.Author == rule.Value
+			// A substring of an address cannot be decoded, so this stays a text match.
+			// An author rule naming a whole address must use "eq" to survive the two
+			// renderings above.
+			return strings.Contains(app.Author, rule.Value)
 		}
 	}
 
diff --git a/content_filter_rules_test.go b/content_filter_rules_test.go
new file mode 100644
index 0000000..cae60b3
--- /dev/null
+++ b/content_filter_rules_test.go
@@ -0,0 +1,109 @@
+// Copyright 2025 HOLOGRAM Project. All rights reserved.
+// Regression tests for evaluateRule's author and category rules (issue #27).
+
+package main
+
+import "testing"
+
+// Two renderings of ONE key. A contract stores the dero1 form on every network,
+// because ADDRESS_STRING builds through rpc.NewAddressFromKeys and leaves Mainnet
+// true; consensus cannot depend on which network a node believes it is on. A wallet
+// opened on a simulator shows the deto1 form of the same key. Addresses are bech32,
+// so the prefix names the network and the checksum is computed over it: both halves
+// of the string differ.
+const (
+	authorMainnet   = "dero1qyw4fl3dupcg5qlrcsvcedze507q9u67lxfpu8kgnzp04aq73yheqqg2ctjn4"
+	authorSimulator = "deto1qyw4fl3dupcg5qlrcsvcedze507q9u67lxfpu8kgnzp04aq73yheqqgsph2ka"
+	otherAuthor     = "dero1qy976ssakhfynpd4lnh39u7gw9spfzr9z55ckfd0yhrhsdr235glgqq28xlvm"
+)
+
+func ruleFor(t, op, v string) FilterRule {
+	return FilterRule{Type: t, Operator: op, Value: v, Enabled: true}
+}
+
+// TestAuthorRuleEqMatchesAcrossNetworkRendering is the half of issue #27 that made an
+// author rule unusable the moment anyone could write one: the rule value is whatever
+// the user copied out of their wallet, and the app's author is whatever the contract
+// stored, so on a simulator the two are the same key spelled two ways.
+func TestAuthorRuleEqMatchesAcrossNetworkRendering(t *testing.T) {
+	if authorMainnet == authorSimulator {
+		t.Fatal("the two vectors are identical; this test proves nothing")
+	}
+
+	cases := []struct {
+		name      string
+		appAuthor string
+		ruleValue string
+		wantMatch bool
+	}{
+		{"same rendering", authorMainnet, authorMainnet, true},
+		{"app mainnet, rule simulator", authorMainnet, authorSimulator, true},
+		{"app simulator, rule mainnet", authorSimulator, authorMainnet, true},
+		{"different author", authorMainnet, otherAuthor, false},
+		{"different author across networks", authorSimulator, otherAuthor, false},
+		{"rule is not an address", authorMainnet, "nobody", false},
+		{"app author empty", "", authorMainnet, false},
+	}
+
+	f := &ContentFilter{}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			app := AppInfo{Author: tc.appAuthor}
+			got := f.evaluateRule(ruleFor("author", "eq", tc.ruleValue), app, 0)
+			if got != tc.wantMatch {
+				t.Fatalf("author eq %q vs %q = %v, want %v",
+					tc.appAuthor, tc.ruleValue, got, tc.wantMatch)
+			}
+		})
+	}
+}
+
+// TestContainsOperatorIsSubstring is the other half of issue #27: both contains arms
+// were a copy of their eq arm, so "contains" behaved as exact equality and a rule
+// using it could never match a longer string.
+func TestContainsOperatorIsSubstring(t *testing.T) {
+	f := &ContentFilter{}
+
+	cases := []struct {
+		name      string
+		ruleType  string
+		app       AppInfo
+		value     string
+		wantMatch bool
+	}{
+		{"category substring", "category", AppInfo{Category: "games/arcade"}, "arcade", true},
+		{"category exact still matches", "category", AppInfo{Category: "games"}, "games", true},
+		{"category absent", "category", AppInfo{Category: "games"}, "finance", false},
+		{"author substring", "author", AppInfo{Author: authorMainnet}, "qyw4fl3", true},
+		{"author absent", "author", AppInfo{Author: authorMainnet}, "zzzzzz", false},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := f.evaluateRule(ruleFor(tc.ruleType, "contains", tc.value), tc.app, 0)
+			if got != tc.wantMatch {
+				t.Fatalf("%s contains %q = %v, want %v", tc.ruleType, tc.value, got, tc.wantMatch)
+			}
+		})
+	}
+
+	// Non-vacuity: the substring cases above must be ones an equality compare would
+	// REJECT, or this test would pass against the defect it exists to catch.
+	if "games/arcade" == "arcade" || authorMainnet == "qyw4fl3" {
+		t.Fatal("the substring vectors are exact matches; this test cannot see the defect")
+	}
+}
+
+// TestUnknownRuleShapesStayClosed pins the surrounding behaviour the fix must not
+// widen: an unknown type or operator matches nothing.
+func TestUnknownRuleShapesStayClosed(t *testing.T) {
+	f := &ContentFilter{}
+	app := AppInfo{Author: authorMainnet, Category: "games"}
+
+	if f.evaluateRule(ruleFor("keyword", "eq", "games"), app, 0) {
+		t.Fatal("an unimplemented rule type must not match")
+	}
+	if f.evaluateRule(ruleFor("author", "not_contains", authorMainnet), app, 0) {
+		t.Fatal("an unimplemented operator must not match")
+	}
+}