diff --git a/internal/viewer/server.go b/internal/viewer/server.go
index 2f8aa076..182beea5 100644
--- a/internal/viewer/server.go
+++ b/internal/viewer/server.go
@@ -95,6 +95,83 @@ type SeverityCount struct {
 	Low      int
 }
 
+// CategoryCount holds counts for each review comment category.
+type CategoryCount struct {
+	Bug             int
+	Security        int
+	Performance     int
+	Maintainability int
+	Test            int
+	Style           int
+	Documentation   int
+	Other           int
+}
+
+var knownCommentCategories = map[string]struct{}{
+	"bug":             {},
+	"security":        {},
+	"performance":     {},
+	"maintainability": {},
+	"test":            {},
+	"style":           {},
+	"documentation":   {},
+	"other":           {},
+}
+
+func normalizedCommentCategory(category string) string {
+	category = strings.ToLower(strings.TrimSpace(category))
+	if _, ok := knownCommentCategories[category]; ok {
+		return category
+	}
+	return "other"
+}
+
+func normalizedCommentSeverity(severity string) string {
+	return strings.ToLower(strings.TrimSpace(severity))
+}
+
+func categoryCounts(comments []*ReviewComment) CategoryCount {
+	var counts CategoryCount
+	for _, comment := range comments {
+		switch normalizedCommentCategory(comment.Category) {
+		case "bug":
+			counts.Bug++
+		case "security":
+			counts.Security++
+		case "performance":
+			counts.Performance++
+		case "maintainability":
+			counts.Maintainability++
+		case "test":
+			counts.Test++
+		case "style":
+			counts.Style++
+		case "documentation":
+			counts.Documentation++
+		default:
+			counts.Other++
+		}
+	}
+	return counts
+}
+
+func severityCounts(comments []*ReviewComment) SeverityCount {
+	var counts SeverityCount
+	for _, comment := range comments {
+		switch strings.ToLower(strings.TrimSpace(comment.Severity)) {
+		case "critical":
+			counts.Critical++
+		case "high":
+			counts.High++
+		case "medium":
+			counts.Medium++
+		case "low":
+			counts.Low++
+		}
+	}
+	return counts
+}
+
 func parseTemplate(name string) (*template.Template, error) {
 	funcMap := template.FuncMap{
 		"formatDuration": formatDuration,
@@ -164,24 +241,12 @@ func parseTemplate(name string) (*template.Template, error) {
 			}
 			return groups
 		},
-		"severityCounts": func(comments []*ReviewComment) SeverityCount {
-			var sc SeverityCount
-			for _, c := range comments {
-				switch c.Severity {
-				case "critical":
-					sc.Critical++
-				case "high":
-					sc.High++
-				case "medium":
-					sc.Medium++
-				case "low":
-					sc.Low++
-				}
-			}
-			return sc
-		},
+		"severityCounts":  severityCounts,
+		"categoryCounts":  categoryCounts,
+		"commentCategory": normalizedCommentCategory,
+		"commentSeverity": normalizedCommentSeverity,
 		"severityClass": func(s string) string {
-			switch s {
+			switch normalizedCommentSeverity(s) {
 			case "critical":
 				return "severity-critical"
 			case "high":
@@ -195,13 +260,23 @@ func parseTemplate(name string) (*template.Template, error) {
 			}
 		},
 		"categoryClass": func(s string) string {
-			switch s {
+			switch normalizedCommentCategory(s) {
 			case "bug":
 				return "cat-bug"
 			case "security":
 				return "cat-security"
 			case "performance":
 				return "cat-performance"
+			case "maintainability":
+				return "cat-maintainability"
+			case "test":
+				return "cat-test"
+			case "style":
+				return "cat-style"
+			case "documentation":
+				return "cat-documentation"
+			case "other":
+				return "cat-other"
 			default:
 				return "cat-default"
 			}
diff --git a/internal/viewer/server_startserver_test.go b/internal/viewer/server_startserver_test.go
index 1d94ef75..b79e0df4 100644
--- a/internal/viewer/server_startserver_test.go
+++ b/internal/viewer/server_startserver_test.go
@@ -40,8 +40,9 @@ func TestStartServer_AddrInUse(t *testing.T) {
 }
 
 // TestParseTemplate_SessionWithComments renders session.html with review
-// comments spanning every severity and category so the funcMap closures
-// (severityCounts, severityClass, categoryClass, groupCommentsByFile) execute.
+// comments spanning several severities and categories so the template helpers
+// (severityCounts, categoryCounts, severityClass, categoryClass,
+// groupCommentsByFile, and the normalization helpers) execute.
 func TestParseTemplate_SessionWithComments(t *testing.T) {
 	tmpl, err := parseTemplate("session.html")
 	if err != nil {
@@ -71,4 +72,30 @@ func TestParseTemplate_SessionWithComments(t *testing.T) {
 	if !strings.Contains(rr.Body.String(), "Review Comments") {
 		t.Error("rendered page missing Review Comments section")
 	}
+	body := rr.Body.String()
+	for _, want := range []string{
+		`data-filter-kind="all"`,
+		`data-filter-kind="severity" data-filter-value="critical"`,
+		`data-filter-kind="category" data-filter-value="bug"`,
+		`data-filter-kind="category" data-filter-value="other"`,
+		`data-comment-card data-category="bug" data-severity="critical"`,
+		`data-comment-card data-category="other" data-severity="low"`,
+		`data-comment-filter-empty`,
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("rendered page missing %q", want)
+		}
+	}
+}
+
+func TestCategoryCounts_NormalizesUnknownCategories(t *testing.T) {
+	counts := categoryCounts([]*ReviewComment{
+		{Category: "bug"},
+		{Category: "MAINTAINABILITY"},
+		{Category: ""},
+		{Category: "not-a-category"},
+	})
+	if counts.Bug != 1 || counts.Maintainability != 1 || counts.Other != 2 {
+		t.Fatalf("unexpected category counts: %+v", counts)
+	}
 }
diff --git a/internal/viewer/static/session.js b/internal/viewer/static/session.js
index bbc970d8..33b34fce 100644
--- a/internal/viewer/static/session.js
+++ b/internal/viewer/static/session.js
@@ -28,3 +28,72 @@ document.querySelectorAll('.response-text').forEach(function(el) {
     });
     el.innerHTML = html;
 });
+
+(function() {
+    const filters = Array.from(document.querySelectorAll('.comment-filter-chip[data-filter-kind]'));
+    const groups = Array.from(document.querySelectorAll('.comment-file-group'));
+    const emptyState = document.querySelector('[data-comment-filter-empty]');
+
+    if (filters.length === 0 || groups.length === 0) {
+        return;
+    }
+
+    let activeKind = 'all';
+    let activeValue = '';
+
+    function cardMatches(card) {
+        if (activeKind === 'all') {
+            return true;
+        }
+        return card.dataset[activeKind] === activeValue;
+    }
+
+    function updateFilterState() {
+        filters.forEach(function(filter) {
+            const isActive = activeKind === filter.dataset.filterKind &&
+                activeValue === (filter.dataset.filterValue || '');
+            filter.classList.toggle('is-active', isActive);
+            filter.setAttribute('aria-pressed', String(isActive));
+        });
+
+        let visibleCount = 0;
+        groups.forEach(function(group) {
+            const cards = Array.from(group.querySelectorAll('[data-comment-card]'));
+            let groupVisibleCount = 0;
+            cards.forEach(function(card) {
+                const visible = cardMatches(card);
+                card.hidden = !visible;
+                if (visible) {
+                    groupVisibleCount++;
+                    visibleCount++;
+                }
+            });
+            group.hidden = groupVisibleCount === 0;
+            const count = group.querySelector('[data-comment-count]');
+            if (count) {
+                count.textContent = groupVisibleCount + ' comment' + (groupVisibleCount === 1 ? '' : 's');
+            }
+        });
+
+        if (emptyState) {
+            emptyState.hidden = visibleCount !== 0;
+        }
+    }
+
+    filters.forEach(function(filter) {
+        filter.addEventListener('click', function() {
+            const kind = filter.dataset.filterKind;
+            const value = filter.dataset.filterValue || '';
+            if (kind === 'all' || (activeKind === kind && activeValue === value)) {
+                activeKind = 'all';
+                activeValue = '';
+            } else {
+                activeKind = kind;
+                activeValue = value;
+            }
+            updateFilterState();
+        });
+    });
+
+    updateFilterState();
+})();
diff --git a/internal/viewer/static/style.css b/internal/viewer/static/style.css
index 1fab6efc..9bae9bb7 100644
--- a/internal/viewer/static/style.css
+++ b/internal/viewer/static/style.css
@@ -885,6 +885,40 @@ p {
     gap: 0.5rem;
     margin-bottom: 1.25rem;
 }
+.comment-filter-bar {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 0.5rem;
+    margin-bottom: 0.65rem;
+}
+.category-filters {
+    margin-bottom: 1.25rem;
+}
+.comment-filter-chip {
+    appearance: none;
+    border: 1px solid transparent;
+    border-radius: 20px;
+    padding: 0.3em 0.75em;
+    font: inherit;
+    font-size: 0.75rem;
+    font-weight: 600;
+    letter-spacing: 0.01em;
+    line-height: 1.35;
+    cursor: pointer;
+    transition: opacity var(--transition), box-shadow var(--transition), border-color var(--transition);
+}
+.comment-filter-chip:not(.is-active) { opacity: 0.72; }
+.comment-filter-chip:hover,
+.comment-filter-chip.is-active { opacity: 1; }
+.comment-filter-chip.is-active {
+    border-color: currentColor;
+    box-shadow: 0 0 0 2px var(--surface), 0 0 0 3px currentColor;
+}
+.comment-filter-chip:focus-visible {
+    outline: 2px solid var(--link);
+    outline-offset: 2px;
+}
+.filter-all { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
 .severity-badge {
     padding: 0.3em 0.75em;
     border-radius: 20px;
@@ -970,6 +1004,11 @@ p {
 .cat-bug { background: #fef2f2; color: #dc2626; }
 .cat-security { background: #fdf2f8; color: #be185d; }
 .cat-performance { background: #fff7ed; color: #ea580c; }
+.cat-maintainability { background: #eff6ff; color: #2563eb; }
+.cat-test { background: #f0fdf4; color: #15803d; }
+.cat-style { background: #f5f3ff; color: #7c3aed; }
+.cat-documentation { background: #ecfeff; color: #0e7490; }
+.cat-other { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
 .cat-default { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
 .severity-default { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
 
@@ -977,9 +1016,21 @@ p {
     .cat-bug { background: rgba(220, 38, 38, 0.12); color: #fca5a5; }
     .cat-security { background: rgba(190, 24, 93, 0.12); color: #f9a8d4; }
     .cat-performance { background: rgba(234, 88, 12, 0.12); color: #fdba74; }
+    .cat-maintainability { background: rgba(37, 99, 235, 0.12); color: #93c5fd; }
+    .cat-test { background: rgba(21, 128, 61, 0.12); color: #86efac; }
+    .cat-style { background: rgba(124, 58, 237, 0.12); color: #c4b5fd; }
+    .cat-documentation { background: rgba(14, 116, 144, 0.12); color: #67e8f9; }
+    .cat-other { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
     .cat-default { background: var(--badge-neutral-bg); color: var(--badge-neutral-fg); }
 }
 
+.comment-filter-empty {
+    margin: 1.25rem 0 0;
+    color: var(--text-muted);
+    text-align: center;
+    font-size: 0.85rem;
+}
+
 .comment-lines {
     font-family: var(--mono);
     font-size: 0.72rem;
diff --git a/internal/viewer/templates/session.html b/internal/viewer/templates/session.html
index a6adfbce..52a75273 100644
--- a/internal/viewer/templates/session.html
+++ b/internal/viewer/templates/session.html
@@ -110,11 +110,24 @@ <h3>Token Usage</h3>
 <div class="comments-section">
     <h3>Review Comments ({{len .Session.Comments}} findings)</h3>
     {{with severityCounts .Session.Comments}}
-    <div class="severity-bar">
-        {{if .Critical}}<span class="severity-badge severity-critical">Critical: {{.Critical}}</span>{{end}}
-        {{if .High}}<span class="severity-badge severity-high">High: {{.High}}</span>{{end}}
-        {{if .Medium}}<span class="severity-badge severity-medium">Medium: {{.Medium}}</span>{{end}}
-        {{if .Low}}<span class="severity-badge severity-low">Low: {{.Low}}</span>{{end}}
+    <div class="comment-filter-bar severity-filters" aria-label="Filter comments by severity">
+        <button type="button" class="comment-filter-chip filter-all is-active" data-filter-kind="all" data-filter-value="" aria-pressed="true">All: {{len $.Session.Comments}}</button>
+        {{if .Critical}}<button type="button" class="comment-filter-chip severity-critical" data-filter-kind="severity" data-filter-value="critical" aria-pressed="false">Critical: {{.Critical}}</button>{{end}}
+        {{if .High}}<button type="button" class="comment-filter-chip severity-high" data-filter-kind="severity" data-filter-value="high" aria-pressed="false">High: {{.High}}</button>{{end}}
+        {{if .Medium}}<button type="button" class="comment-filter-chip severity-medium" data-filter-kind="severity" data-filter-value="medium" aria-pressed="false">Medium: {{.Medium}}</button>{{end}}
+        {{if .Low}}<button type="button" class="comment-filter-chip severity-low" data-filter-kind="severity" data-filter-value="low" aria-pressed="false">Low: {{.Low}}</button>{{end}}
+    </div>
+    {{end}}
+    {{with categoryCounts .Session.Comments}}
+    <div class="comment-filter-bar category-filters" aria-label="Filter comments by category">
+        {{if .Bug}}<button type="button" class="comment-filter-chip cat-bug" data-filter-kind="category" data-filter-value="bug" aria-pressed="false">Bug: {{.Bug}}</button>{{end}}
+        {{if .Security}}<button type="button" class="comment-filter-chip cat-security" data-filter-kind="category" data-filter-value="security" aria-pressed="false">Security: {{.Security}}</button>{{end}}
+        {{if .Performance}}<button type="button" class="comment-filter-chip cat-performance" data-filter-kind="category" data-filter-value="performance" aria-pressed="false">Performance: {{.Performance}}</button>{{end}}
+        {{if .Maintainability}}<button type="button" class="comment-filter-chip cat-maintainability" data-filter-kind="category" data-filter-value="maintainability" aria-pressed="false">Maintainability: {{.Maintainability}}</button>{{end}}
+        {{if .Test}}<button type="button" class="comment-filter-chip cat-test" data-filter-kind="category" data-filter-value="test" aria-pressed="false">Test: {{.Test}}</button>{{end}}
+        {{if .Style}}<button type="button" class="comment-filter-chip cat-style" data-filter-kind="category" data-filter-value="style" aria-pressed="false">Style: {{.Style}}</button>{{end}}
+        {{if .Documentation}}<button type="button" class="comment-filter-chip cat-documentation" data-filter-kind="category" data-filter-value="documentation" aria-pressed="false">Documentation: {{.Documentation}}</button>{{end}}
+        {{if .Other}}<button type="button" class="comment-filter-chip cat-other" data-filter-kind="category" data-filter-value="other" aria-pressed="false">Other: {{.Other}}</button>{{end}}
     </div>
     {{end}}
     <div class="comment-groups">
@@ -123,11 +136,11 @@ <h3>Review Comments ({{len .Session.Comments}} findings)</h3>
         <summary class="comment-file-header">
             <span class="chevron"></span>
             <span class="file-path">{{.FilePath}}</span>
-            <span class="file-count-badge">{{len .Comments}} comments</span>
+            <span class="file-count-badge" data-comment-count>{{len .Comments}} comments</span>
         </summary>
         <div class="comment-file-body">
         {{range .Comments}}
-            <div class="comment-card">
+            <div class="comment-card" data-comment-card data-category="{{commentCategory .Category}}" data-severity="{{commentSeverity .Severity}}">
                 <div class="comment-meta">
                     {{if .Category}}<span class="comment-badge {{categoryClass .Category}}">{{.Category}}</span>{{end}}
                     {{if .Severity}}<span class="comment-badge {{severityClass .Severity}}">{{.Severity}}</span>{{end}}
@@ -156,6 +169,7 @@ <h3>Review Comments ({{len .Session.Comments}} findings)</h3>
     </details>
     {{end}}
     </div>
+    <p class="comment-filter-empty" data-comment-filter-empty hidden>No comments match this filter.</p>
 </div>
 {{end}}