diff --git a/web/src/composables/useLLMQueryBuilder.ts b/web/src/composables/useLLMQueryBuilder.ts
new file mode 100644
index 0000000..f769d1e
--- /dev/null
+++ b/web/src/composables/useLLMQueryBuilder.ts
@@ -0,0 +1,92 @@
+// web/src/composables/useLLMQueryBuilder.ts
+// BSL 1.1 License
+/**
+ * State and API call logic for the LLM query builder panel.
+ */
+import { ref } from 'vue'
+import { useSearchStore, type SearchParamsResult } from '@/stores/search'
+
+export type BuildStatus = 'idle' | 'thinking' | 'done' | 'error'
+
+const LS_AUTORUN_KEY = 'snipe:llm-autorun'
+
+// Module-level refs so state persists across component re-renders
+const isOpen = ref(false)
+const isLoading = ref(false)
+const status = ref<BuildStatus>('idle')
+const explanation = ref<string>('')
+const error = ref<string | null>(null)
+const autoRun = ref<boolean>(localStorage.getItem(LS_AUTORUN_KEY) === 'true')
+
+export function useLLMQueryBuilder() {
+  const store = useSearchStore()
+
+  function toggle() {
+    isOpen.value = !isOpen.value
+    if (!isOpen.value) {
+      status.value = 'idle'
+      error.value = null
+      explanation.value = ''
+    }
+  }
+
+  function setAutoRun(value: boolean) {
+    autoRun.value = value
+    localStorage.setItem(LS_AUTORUN_KEY, value ? 'true' : 'false')
+  }
+
+  async function buildQuery(naturalLanguage: string): Promise<SearchParamsResult | null> {
+    if (!naturalLanguage.trim()) return null
+
+    isLoading.value = true
+    status.value = 'thinking'
+    error.value = null
+    explanation.value = ''
+
+    try {
+      const resp = await fetch('/api/search/build', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ natural_language: naturalLanguage.trim() }),
+      })
+
+      if (!resp.ok) {
+        const data = await resp.json().catch(() => ({}))
+        const msg = typeof data.detail === 'string'
+          ? data.detail
+          : (data.detail?.message ?? `Server error (${resp.status})`)
+        throw new Error(msg)
+      }
+
+      const params: SearchParamsResult = await resp.json()
+      store.populateFromLLM(params)
+      explanation.value = params.explanation
+      status.value = 'done'
+
+      if (autoRun.value) {
+        await store.search(params.base_query, store.filters.value)
+      }
+
+      return params
+    } catch (err: unknown) {
+      const msg = err instanceof Error ? err.message : 'Something went wrong.'
+      error.value = msg
+      status.value = 'error'
+      return null
+    } finally {
+      isLoading.value = false
+    }
+  }
+
+  return {
+    isOpen,
+    isLoading,
+    status,
+    explanation,
+    error,
+    autoRun,
+    toggle,
+    setAutoRun,
+    buildQuery,
+  }
+}