diff --git a/src/renderer/components/sidebar/FilterInput.js b/src/renderer/components/sidebar/FilterInput.js
index a8ecf793..5bc95c60 100644
--- a/src/renderer/components/sidebar/FilterInput.js
+++ b/src/renderer/components/sidebar/FilterInput.js
@@ -48,10 +48,14 @@ export const FilterInput = props => {
   }
 
   const handleTagClick = tag => {
-    const tagFilter = `#${tag}`
-    const newFilter = search.filter
-      ? `${search.filter} ${tagFilter}`
-      : tagFilter
+    const tagFilter = `#${tag.toUpperCase()}`
+    const tokens = search.filter.split(' ').filter(Boolean)
+    const tagIndex = tokens.findIndex(t => t.toUpperCase() === tagFilter)
+
+    const newFilter = tagIndex >= 0
+      ? tokens.filter((_, i) => i !== tagIndex).join(' ')
+      : search.filter ? `${search.filter} ${tagFilter}` : tagFilter
+
     setCursor(null)
     setSearch({ ...search, filter: newFilter, force: true })
   }
diff --git a/src/renderer/store/MiniSearch.js b/src/renderer/store/MiniSearch.js
index 9be22bb8..c9b845d2 100644
--- a/src/renderer/store/MiniSearch.js
+++ b/src/renderer/store/MiniSearch.js
@@ -40,8 +40,8 @@ export const parseQuery = (terms, ids = []) => {
       // Remove hyphens to match the extractField transformation for scope
       const scopeValue = token.substring(1).replace(/-/g, '')
       scopeValue.length > 1 && acc.scope.push(scopeValue)
-    } else if (token.startsWith('-#')) token.length > 3 && acc.excludeTags.push(token.substring(2).toLowerCase())
-    else if (token.startsWith('#')) token.length > 2 && acc.tags.push(token.substring(1))
+    } else if (token.startsWith('-#')) token.length > 2 && acc.excludeTags.push(token.substring(2))
+    else if (token.startsWith('#')) token.length > 1 && acc.tags.push(token.substring(1))
     else if (token.startsWith('!')) token.length > 2 && acc.ids.push(token.substring(1))
     else if (token.startsWith('&')) { /* ignore */ } else if (token) acc.text.push(token)
     return acc
@@ -57,7 +57,7 @@ export const parseQuery = (terms, ids = []) => {
 
   add('scope', 'OR')
   add('text', 'AND', true)
-  add('tags', 'AND', true)
+  add('tags', 'AND')
 
   const filter = parts.ids.length
     ? result => parts.ids.some(id => result.id.startsWith(id))
diff --git a/src/renderer/store/SearchIndex.js b/src/renderer/store/SearchIndex.js
index 95343c19..45367d12 100644
--- a/src/renderer/store/SearchIndex.js
+++ b/src/renderer/store/SearchIndex.js
@@ -234,8 +234,8 @@ SearchIndex.prototype.search = async function (terms, options) {
     ? matches.filter(match => {
       const doc = this.cachedDocuments[match.id]
       if (!doc || !doc.tags) return true
-      const docTags = doc.tags.filter(Boolean).map(t => t.toLowerCase())
-      return !excludeTags.some(tag => docTags.includes(tag))
+      const docTags = doc.tags.filter(Boolean).map(t => t.toUpperCase())
+      return !excludeTags.some(tag => docTags.includes(tag.toUpperCase()))
     })
     : matches
 
diff --git a/test/renderer/store/MiniSearch-test.js b/test/renderer/store/MiniSearch-test.js
index 8efd717b..6106090f 100644
--- a/test/renderer/store/MiniSearch-test.js
+++ b/test/renderer/store/MiniSearch-test.js
@@ -54,5 +54,33 @@ describe('MiniSearch', function () {
       const actual = index.search(query)
       assert.strictEqual(actual.length, _3OSC.docs.length - 1) // minus one installation
     })
+
+    it('tag search uses exact matching, not prefix matching', function () {
+      const index = createIndex()
+      index.addAll([
+        { id: 'feature:1', text: 'First feature', tags: ['A'] },
+        { id: 'feature:2', text: 'Second feature', tags: ['AA'] },
+        { id: 'feature:3', text: 'Third feature', tags: ['AAA'] }
+      ])
+
+      const searchTag = (tag) => {
+        const [query] = parseQuery(tag)
+        return index.search(query).map(({ id }) => id).sort()
+      }
+
+      // Each tag search should only return exact matches
+      assert.deepStrictEqual(searchTag('#A'), ['feature:1'])
+      assert.deepStrictEqual(searchTag('#AA'), ['feature:2'])
+      assert.deepStrictEqual(searchTag('#AAA'), ['feature:3'])
+    })
+
+    it('single-letter exclude tags are parsed correctly', function () {
+      // Verify parseQuery handles single-letter exclude tags
+      const [, options] = parseQuery('-#A')
+      assert.deepStrictEqual(options.excludeTags, ['A'])
+
+      const [, options2] = parseQuery('-#B -#C')
+      assert.deepStrictEqual(options2.excludeTags, ['B', 'C'])
+    })
   })
 })