diff --git a/plugins/toolbox-search/src/block_searcher.ts b/plugins/toolbox-search/src/block_searcher.ts
index d04f9b53f..005974b73 100644
--- a/plugins/toolbox-search/src/block_searcher.ts
+++ b/plugins/toolbox-search/src/block_searcher.ts
@@ -113,7 +113,7 @@ export class BlockSearcher {
     if (normalizedInput.length <= 3) return [normalizedInput];
 
     const trigrams: string[] = [];
-    for (let start = 0; start < normalizedInput.length - 3; start++) {
+    for (let start = 0; start <= normalizedInput.length - 3; start++) {
       trigrams.push(normalizedInput.substring(start, start + 3));
     }
 
diff --git a/plugins/toolbox-search/test/tests.mocha.js b/plugins/toolbox-search/test/tests.mocha.js
index 3699ee177..1c4ae96f0 100644
--- a/plugins/toolbox-search/test/tests.mocha.js
+++ b/plugins/toolbox-search/test/tests.mocha.js
@@ -15,6 +15,15 @@ suite('Toolbox search', () => {
 });
 
 suite('BlockSearcher', () => {
+  test('generateTrigrams handles empty and short input', () => {
+    const searcher = new BlockSearcher();
+    const generateTrigrams = searcher.generateTrigrams.bind(searcher);
+
+    assert.deepEqual(generateTrigrams(''), []);
+    assert.deepEqual(generateTrigrams('a'), ['a']);
+    assert.deepEqual(generateTrigrams('abc'), ['abc']);
+  });
+
   test('indexes the default value of dropdown fields', () => {
     const searcher = new BlockSearcher();
     const blocks = [
@@ -57,6 +66,119 @@ suite('BlockSearcher', () => {
     assert.sameMembers(ransomNoteMatches, [listCreateWithBlock]);
   });
 
+  test('requires the final trigram when matching longer queries', () => {
+    const searcher = new BlockSearcher();
+    const mathConstrainBlock = {
+      kind: 'block',
+      type: 'math_constrain',
+    };
+    searcher.indexBlocks([mathConstrainBlock]);
+
+    const matches = searcher.blockTypesMatching('conso');
+
+    assert.notInclude(
+      matches,
+      mathConstrainBlock,
+      'query missing trailing trigram should not match',
+    );
+  });
+
+  test('normalizes underscores in block types to spaces', () => {
+    if (!Blockly.Blocks['searcher_underscore_block']) {
+      Blockly.defineBlocksWithJsonArray([
+        {
+          type: 'searcher_underscore_block',
+          message0: 'custom block with underscore',
+        },
+      ]);
+    }
+
+    const searcher = new BlockSearcher();
+    const blockInfo = {
+      kind: 'block',
+      type: 'searcher_underscore_block',
+    };
+    searcher.indexBlocks([blockInfo]);
+
+    assert.sameMembers(
+      searcher.blockTypesMatching('custom block with underscore'),
+      [blockInfo],
+    );
+    assert.isEmpty(searcher.blockTypesMatching('custom_block_with_underscore'));
+  });
+
+  test('longer queries disambiguate similar blocks', () => {
+    if (!Blockly.Blocks['searcher_charlie']) {
+      Blockly.defineBlocksWithJsonArray([
+        {
+          type: 'searcher_charlie',
+          message0: 'alpha bravo charlie',
+        },
+        {
+          type: 'searcher_delta',
+          message0: 'alpha bravo delta',
+        },
+      ]);
+    }
+
+    const searcher = new BlockSearcher();
+    const blockA = {kind: 'block', type: 'searcher_charlie'};
+    const blockB = {kind: 'block', type: 'searcher_delta'};
+
+    searcher.indexBlocks([blockA, blockB]);
+
+    const broadQueryMatches = searcher.blockTypesMatching('alpha bravo');
+    assert.sameMembers(broadQueryMatches, [blockA, blockB]);
+
+    const specificQueryMatches =
+      searcher.blockTypesMatching('alpha bravo charlie');
+    assert.sameMembers(specificQueryMatches, [blockA]);
+  });
+
+  test('indexes dropdown alt text options', () => {
+    if (!Blockly.Blocks['searcher_dropdown_alt']) {
+      Blockly.defineBlocksWithJsonArray([
+        {
+          type: 'searcher_dropdown_alt',
+          message0: 'weather %1',
+          args0: [
+            {
+              type: 'field_dropdown',
+              name: 'WEATHER',
+              options: [
+                [
+                  {
+                    src: 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEA',
+                    width: 1,
+                    height: 1,
+                    alt: 'Sunny',
+                  },
+                  'SUN',
+                ],
+                [
+                  {
+                    src: 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEA',
+                    width: 1,
+                    height: 1,
+                    alt: 'Cloudy',
+                  },
+                  'CLOUD',
+                ],
+              ],
+            },
+          ],
+        },
+      ]);
+    }
+
+    const searcher = new BlockSearcher();
+    const blockInfo = {kind: 'block', type: 'searcher_dropdown_alt'};
+    searcher.indexBlocks([blockInfo]);
+
+    assert.sameMembers(searcher.blockTypesMatching('sunny'), [blockInfo]);
+    assert.sameMembers(searcher.blockTypesMatching('cloudy'), [blockInfo]);
+  });
+
   test('returns an empty list when no matches are found', () => {
     const searcher = new BlockSearcher();
     assert.isEmpty(searcher.blockTypesMatching('abc123'));