diff --git a/src/App.css b/src/App.css
index cafb124..5e9b290 100644
--- a/src/App.css
+++ b/src/App.css
@@ -201,6 +201,22 @@ body {
   }
 }
 
+/* Auto-solve blink animation */
+.cell.auto-blinking .cell-value {
+  animation: autoFillBlink 0.4s ease-in-out infinite;
+}
+
+@keyframes autoFillBlink {
+  0%, 100% {
+    opacity: 1;
+    text-shadow: 0 0 10px rgba(255, 152, 0, 0.7);
+  }
+  50% {
+    opacity: 0.25;
+    text-shadow: 0 0 0 transparent;
+  }
+}
+
 @keyframes celebrateText {
   0% {
     transform: scale(1);
diff --git a/src/App.jsx b/src/App.jsx
index fd53d49..3ee73f7 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -7,6 +7,7 @@ import WinModal from './components/WinModal'
 import Confetti from './components/Confetti'
 import SettingsModal from './components/SettingsModal'
 import { useGame } from './hooks/useGame'
+import { findCertainMove } from './utils/sudoku'
 
 function App() {
   const {
@@ -23,6 +24,7 @@ function App() {
     toggleDarkMode,
     undo,
     redo,
+    autoFill,
   } = useGame()
 
   const [showSettings, setShowSettings] = useState(false)
@@ -30,6 +32,10 @@ function App() {
     const saved = parseInt(localStorage.getItem('sudoku-hue'), 10)
     return isNaN(saved) ? 211 : saved
   })
+  const [solveUnlocked, setSolveUnlocked] = useState(false)
+  const [autoSolving, setAutoSolving] = useState(false)
+  const [autoBlinkCell, setAutoBlinkCell] = useState(null)
+  const [autoCooldown, setAutoCooldown] = useState(false)
 
   useEffect(() => {
     document.body.style.background = state.darkMode ? '#1a1a2e' : '#f8f9fa'
@@ -50,6 +56,71 @@ function App() {
     return () => window.removeEventListener('keydown', handleKeyDown)
   }, [])
 
+  useEffect(() => {
+    if (solveUnlocked) return
+    const sequence = [
+      'ArrowUp', 'ArrowUp', 'ArrowDown', 'ArrowDown',
+      'ArrowLeft', 'ArrowRight', 'ArrowLeft', 'ArrowRight',
+      'b', 'a',
+    ]
+    let progress = 0
+    function onKeyDown(e) {
+      const expected = sequence[progress]
+      const key = expected.length === 1 ? e.key.toLowerCase() : e.key
+      if (key === expected) {
+        progress++
+        if (progress === sequence.length) {
+          setSolveUnlocked(true)
+        }
+      } else {
+        progress = key === sequence[0] ? 1 : 0
+      }
+    }
+    window.addEventListener('keydown', onKeyDown)
+    return () => window.removeEventListener('keydown', onKeyDown)
+  }, [solveUnlocked])
+
+  useEffect(() => {
+    if (!autoSolving) {
+      setAutoBlinkCell(null)
+      setAutoCooldown(false)
+    }
+  }, [autoSolving])
+
+  useEffect(() => {
+    if (!autoSolving) return
+    if (state.isComplete) {
+      setAutoSolving(false)
+      return
+    }
+    if (autoBlinkCell || autoCooldown) return
+
+    const move = findCertainMove(state.board)
+    if (!move) {
+      setAutoSolving(false)
+      return
+    }
+    autoFill(move.row, move.col, move.value)
+    setAutoBlinkCell({ row: move.row, col: move.col })
+  }, [autoSolving, state.board, state.isComplete, autoBlinkCell, autoCooldown, autoFill])
+
+  useEffect(() => {
+    if (!autoBlinkCell) return
+    const blinkMs = 1000 + Math.random() * 1000
+    const t = setTimeout(() => {
+      setAutoBlinkCell(null)
+      setAutoCooldown(true)
+    }, blinkMs)
+    return () => clearTimeout(t)
+  }, [autoBlinkCell])
+
+  useEffect(() => {
+    if (!autoCooldown) return
+    const cooldownMs = 1000 + Math.random() * 1000
+    const t = setTimeout(() => setAutoCooldown(false), cooldownMs)
+    return () => clearTimeout(t)
+  }, [autoCooldown])
+
   return (
     <div className={`app${state.darkMode ? ' dark' : ''}`} style={{ '--hue': hue }}>
       <header className="app-header">
@@ -73,6 +144,7 @@ function App() {
           highlightedNumber={state.highlightedNumber}
           showErrors={state.showErrors}
           celebrating={state.showEffects ? state.celebrating : new Set()}
+          autoBlinkCell={autoBlinkCell}
           selectCell={selectCell}
           deselect={deselect}
         />
@@ -92,6 +164,9 @@ function App() {
           canUndo={state.history.length > 0}
           canRedo={state.future.length > 0}
           onOpenSettings={() => setShowSettings(true)}
+          solveUnlocked={solveUnlocked}
+          autoSolving={autoSolving}
+          onToggleAutoSolve={() => setAutoSolving(s => !s)}
         />
       </main>
 
diff --git a/src/components/Board.jsx b/src/components/Board.jsx
index 348e4a5..db30183 100644
--- a/src/components/Board.jsx
+++ b/src/components/Board.jsx
@@ -2,7 +2,7 @@ import React from 'react'
 import Cell from './Cell'
 import { checkValue } from '../utils/sudoku'
 
-function Board({ board, puzzle, solution, notes, selected, highlightedNumber, showErrors, celebrating, selectCell, deselect }) {
+function Board({ board, puzzle, solution, notes, selected, highlightedNumber, showErrors, celebrating, autoBlinkCell, selectCell, deselect }) {
   const selectedValue = selected && board[selected.row][selected.col]
   const activeNumber = selected ? selectedValue : highlightedNumber
 
@@ -31,6 +31,8 @@ function Board({ board, puzzle, solution, notes, selected, highlightedNumber, sh
             value !== 0 &&
             !checkValue(solution, r, c, value)
           const isCelebrating = celebrating.has(`${r},${c}`)
+          const isAutoBlinking =
+            autoBlinkCell && autoBlinkCell.row === r && autoBlinkCell.col === c
 
           return (
             <Cell
@@ -45,6 +47,7 @@ function Board({ board, puzzle, solution, notes, selected, highlightedNumber, sh
               isSameNumber={isSameNumber}
               isError={isError}
               isCelebrating={isCelebrating}
+              isAutoBlinking={isAutoBlinking}
               onClick={(e) => e.ctrlKey || e.metaKey ? deselect() : selectCell(r, c)}
             />
           )
diff --git a/src/components/Cell.jsx b/src/components/Cell.jsx
index b2f051b..428c561 100644
--- a/src/components/Cell.jsx
+++ b/src/components/Cell.jsx
@@ -1,6 +1,6 @@
 import React from 'react'
 
-function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlightedCol, isHighlightedBox, isSameNumber, isError, isCelebrating, onClick }) {
+function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlightedCol, isHighlightedBox, isSameNumber, isError, isCelebrating, isAutoBlinking, onClick }) {
   const classes = ['cell']
   if (isGiven) classes.push('given')
   if (isSelected) classes.push('selected')
@@ -10,6 +10,7 @@ function Cell({ value, notes, isGiven, isSelected, isHighlightedRow, isHighlight
   if (isSameNumber) classes.push('same-number')
   if (isError) classes.push('error')
   if (isCelebrating) classes.push('celebrating')
+  if (isAutoBlinking) classes.push('auto-blinking')
 
   return (
     <div className={classes.join(' ')} onClick={onClick}>
diff --git a/src/components/GameControls.jsx b/src/components/GameControls.jsx
index 979a2d1..4bc812b 100644
--- a/src/components/GameControls.jsx
+++ b/src/components/GameControls.jsx
@@ -8,7 +8,7 @@ const DIFFICULTIES = [
   { value: 'expert', label: 'Expert' },
 ]
 
-function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, canUndo, canRedo, onOpenSettings }) {
+function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, canUndo, canRedo, onOpenSettings, solveUnlocked, autoSolving, onToggleAutoSolve }) {
   const [difficulty, setDifficulty] = useState(currentDifficulty)
   const [showConfirm, setShowConfirm] = useState(false)
 
@@ -32,6 +32,11 @@ function GameControls({ currentDifficulty, onNewGame, onClear, onUndo, onRedo, c
         <button className="btn btn-primary" onClick={() => setShowConfirm(true)}>
           Nova Partida
         </button>
+        {solveUnlocked && (
+          <button className="btn btn-secondary" onClick={onToggleAutoSolve}>
+            {autoSolving ? 'Atura' : 'Resol'}
+          </button>
+        )}
       </div>
       <div className="controls-row">
         <button className="btn btn-secondary" onClick={onClear} title="Esborra">
diff --git a/src/hooks/useGame.js b/src/hooks/useGame.js
index 99011aa..2da7bd5 100644
--- a/src/hooks/useGame.js
+++ b/src/hooks/useGame.js
@@ -243,6 +243,40 @@ function reducer(state, action) {
       }
     }
 
+    case 'AUTO_FILL': {
+      if (state.isComplete) return state
+      const { row, col, value } = action
+      if (state.puzzle[row][col] !== 0) return state
+      if (state.board[row][col] !== 0) return state
+
+      const histUpdate = pushHistory(state)
+      const newBoard = cloneBoard(state.board)
+      const newNotes = cloneNotes(state.notes)
+      newBoard[row][col] = value
+      newNotes[row][col] = new Set()
+
+      const complete = isBoardComplete(newBoard, state.solution)
+
+      const prevKeys = findCompletedGroupKeys(state.board, state.solution)
+      const newKeys = findCompletedGroupKeys(newBoard, state.solution)
+      const freshKeys = new Set()
+      for (const key of newKeys) {
+        if (!prevKeys.has(key)) freshKeys.add(key)
+      }
+      const celebrating = cellsFromGroupKeys(freshKeys)
+
+      return {
+        ...state,
+        ...histUpdate,
+        selected: { row, col },
+        board: newBoard,
+        notes: newNotes,
+        isComplete: complete,
+        isRunning: !complete,
+        celebrating,
+      }
+    }
+
     case 'CLEAR_CELL': {
       if (!state.selected || state.isComplete) return state
       const { row, col } = state.selected
@@ -390,6 +424,10 @@ export function useGame() {
     dispatch({ type: 'REDO' })
   }, [])
 
+  const autoFill = useCallback((row, col, value) => {
+    dispatch({ type: 'AUTO_FILL', row, col, value })
+  }, [])
+
   const moveSelection = useCallback((dr, dc) => {
     dispatch({ type: 'MOVE_SELECTION', dr, dc })
   }, [])
@@ -481,6 +519,7 @@ export function useGame() {
     toggleDarkMode,
     undo,
     redo,
+    autoFill,
   }
 }
 
diff --git a/src/utils/sudoku.js b/src/utils/sudoku.js
index a7b3cea..edda38f 100644
--- a/src/utils/sudoku.js
+++ b/src/utils/sudoku.js
@@ -127,3 +127,83 @@ export function isBoardComplete(board, solution) {
   }
   return true
 }
+
+export function findCertainMove(board) {
+  const candidates = Array.from({ length: 9 }, () =>
+    Array.from({ length: 9 }, () => null)
+  )
+
+  for (let r = 0; r < 9; r++) {
+    for (let c = 0; c < 9; c++) {
+      if (board[r][c] !== 0) continue
+      const cands = new Set([1, 2, 3, 4, 5, 6, 7, 8, 9])
+      for (let i = 0; i < 9; i++) {
+        cands.delete(board[r][i])
+        cands.delete(board[i][c])
+      }
+      const br = Math.floor(r / 3) * 3
+      const bc = Math.floor(c / 3) * 3
+      for (let rr = br; rr < br + 3; rr++) {
+        for (let cc = bc; cc < bc + 3; cc++) {
+          cands.delete(board[rr][cc])
+        }
+      }
+      candidates[r][c] = cands
+    }
+  }
+
+  for (let r = 0; r < 9; r++) {
+    for (let c = 0; c < 9; c++) {
+      const cands = candidates[r][c]
+      if (cands && cands.size === 1) {
+        return { row: r, col: c, value: [...cands][0] }
+      }
+    }
+  }
+
+  for (let r = 0; r < 9; r++) {
+    for (let n = 1; n <= 9; n++) {
+      let count = 0, lastCol = -1
+      for (let c = 0; c < 9; c++) {
+        if (candidates[r][c] && candidates[r][c].has(n)) {
+          count++
+          lastCol = c
+        }
+      }
+      if (count === 1) return { row: r, col: lastCol, value: n }
+    }
+  }
+
+  for (let c = 0; c < 9; c++) {
+    for (let n = 1; n <= 9; n++) {
+      let count = 0, lastRow = -1
+      for (let r = 0; r < 9; r++) {
+        if (candidates[r][c] && candidates[r][c].has(n)) {
+          count++
+          lastRow = r
+        }
+      }
+      if (count === 1) return { row: lastRow, col: c, value: n }
+    }
+  }
+
+  for (let br = 0; br < 3; br++) {
+    for (let bc = 0; bc < 3; bc++) {
+      for (let n = 1; n <= 9; n++) {
+        let count = 0, lastR = -1, lastC = -1
+        for (let r = br * 3; r < br * 3 + 3; r++) {
+          for (let c = bc * 3; c < bc * 3 + 3; c++) {
+            if (candidates[r][c] && candidates[r][c].has(n)) {
+              count++
+              lastR = r
+              lastC = c
+            }
+          }
+        }
+        if (count === 1) return { row: lastR, col: lastC, value: n }
+      }
+    }
+  }
+
+  return null
+}