diff --git a/internal/redundancy/redundancy.go b/internal/redundancy/redundancy.go
index 2b2dd20..ce50833 100644
--- a/internal/redundancy/redundancy.go
+++ b/internal/redundancy/redundancy.go
@@ -16,15 +16,21 @@ type Result struct {
 // Checker detects redundant content at three levels: exact, normalized, and similar.
 // It is safe for concurrent use.
 type Checker struct {
-	mu         sync.Mutex
-	threshold  float64
-	raw        []string
-	normalized []string
+	mu            sync.Mutex
+	threshold     float64
+	raw           []string
+	normalized    []string
+	exactIdx      map[string]bool // O(1) exact lookup
+	normalizedIdx map[string]bool // O(1) normalized lookup
 }
 
 // NewChecker creates a Checker with the given Jaccard similarity threshold.
 func NewChecker(threshold float64) *Checker {
-	return &Checker{threshold: threshold}
+	return &Checker{
+		threshold:     threshold,
+		exactIdx:      make(map[string]bool),
+		normalizedIdx: make(map[string]bool),
+	}
 }
 
 // normalize sorts whitespace-separated tokens so order-independent comparison works.
@@ -38,12 +44,35 @@ func normalize(s string) string {
 func (c *Checker) Record(content string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
+	norm := normalize(content)
 	c.raw = append(c.raw, content)
-	c.normalized = append(c.normalized, normalize(content))
+	c.normalized = append(c.normalized, norm)
+	c.exactIdx[content] = true
+	c.normalizedIdx[norm] = true
 }
 
 // Check tests content against all previously recorded strings.
 // It does NOT record the content — call Record separately if desired.
+func (c *Checker) ExactIndex() map[string]bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	out := make(map[string]bool, len(c.exactIdx))
+	for k, v := range c.exactIdx {
+		out[k] = v
+	}
+	return out
+}
+
+func (c *Checker) NormalizedIndex() map[string]bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	out := make(map[string]bool, len(c.normalizedIdx))
+	for k, v := range c.normalizedIdx {
+		out[k] = v
+	}
+	return out
+}
+
 func (c *Checker) Check(content string) Result {
 	return c.CheckWithThreshold(content, c.threshold)
 }
@@ -55,16 +84,17 @@ func (c *Checker) CheckWithThreshold(content string, threshold float64) Result {
 	defer c.mu.Unlock()
 
 	norm := normalize(content)
-	normTokens := strings.Fields(norm)
 
-	for i, r := range c.raw {
-		if r == content {
-			return Result{IsRedundant: true, Kind: "exact", Similarity: 1.0}
-		}
-		if c.normalized[i] == norm {
-			return Result{IsRedundant: true, Kind: "normalized", Similarity: 1.0}
-		}
-		sim := jaccard(normTokens, strings.Fields(c.normalized[i]))
+	if c.exactIdx[content] {
+		return Result{IsRedundant: true, Kind: "exact", Similarity: 1.0}
+	}
+	if c.normalizedIdx[norm] {
+		return Result{IsRedundant: true, Kind: "normalized", Similarity: 1.0}
+	}
+
+	normTokens := strings.Fields(norm)
+	for _, n := range c.normalized {
+		sim := jaccard(normTokens, strings.Fields(n))
 		if sim >= threshold {
 			return Result{IsRedundant: true, Kind: "similar", Similarity: sim}
 		}
diff --git a/internal/redundancy/redundancy_test.go b/internal/redundancy/redundancy_test.go
index 9dc0be5..3a57f00 100644
--- a/internal/redundancy/redundancy_test.go
+++ b/internal/redundancy/redundancy_test.go
@@ -1,6 +1,7 @@
 package redundancy_test
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/pythondatascrape/engram/internal/redundancy"
@@ -45,3 +46,50 @@ func TestFirstCallNotRedundant(t *testing.T) {
 	result := c.Check("lang=go")
 	require.False(t, result.IsRedundant)
 }
+
+// TestExactLookupUsesIndex verifies that exact duplicates are found via O(1) map lookup.
+// The Checker must expose an ExactIndex() map for inspection.
+func TestExactLookupUsesIndex(t *testing.T) {
+	c := redundancy.NewChecker(0.9)
+	c.Record("lang=go arch=monolith")
+	c.Record("lang=rust framework=axum")
+	idx := c.ExactIndex()
+	require.True(t, idx["lang=go arch=monolith"], "exact index must contain recorded entry")
+	require.True(t, idx["lang=rust framework=axum"], "exact index must contain second entry")
+	require.False(t, idx["lang=go"], "non-recorded string must not appear in exact index")
+}
+
+// TestNormalizedLookupUsesIndex verifies that normalized duplicates are found via O(1) map lookup.
+func TestNormalizedLookupUsesIndex(t *testing.T) {
+	c := redundancy.NewChecker(0.9)
+	c.Record("lang=go arch=monolith")
+	idx := c.NormalizedIndex()
+	// normalized form of "lang=go arch=monolith" is tokens sorted: "arch=monolith lang=go"
+	require.True(t, idx["arch=monolith lang=go"], "normalized index must contain sorted-token form")
+}
+
+// TestLargeExactIndex ensures exact match stays fast with many entries (index must not degrade).
+func TestLargeExactIndex(t *testing.T) {
+	c := redundancy.NewChecker(0.9)
+	const n = 10_000
+	for i := 0; i < n; i++ {
+		c.Record(strings.Repeat("x", i+1))
+	}
+	target := strings.Repeat("x", n/2)
+	result := c.Check(target)
+	require.True(t, result.IsRedundant)
+	require.Equal(t, "exact", result.Kind)
+}
+
+// TestLargeNormalizedIndex ensures normalized match stays fast with many entries.
+func TestLargeNormalizedIndex(t *testing.T) {
+	c := redundancy.NewChecker(0.9)
+	const n = 10_000
+	for i := 0; i < n; i++ {
+		c.Record(strings.Repeat("y", i+1))
+	}
+	// Check reverse-order of a recorded entry — same tokens, different order (single token so same).
+	target := strings.Repeat("y", n/2)
+	result := c.Check(target)
+	require.True(t, result.IsRedundant)
+}