Thermochromic　smart　windows　offer　energy-saving　potential　through　temperature-responsive　optical　transmittance　adjustments,　yet　face　challenges　in　achieving　anti-UV　radiation,　fast　response,　and　high-temperature　stability　characteristics　for　long-term　use.　Herein,　the　rational　design　of　Hofmeister　effect-enhanced,　nanoparticle-shielded　composite　hydrogels,　composed　of　hydroxypropylmethylcellulose　(HPMC),　poly(N,N-dimethylacrylamide)　(PDMAA),　sodium　sulfate,　and　polydopamine　nanoparticles,　for　anti-UV,　fast-response,　and　all-day-modulated　smart　windows　is　reported.　Specifically,　a　three-dimensional　network　of　PDMAA　is　created　as　the　supporting　skeleton,　markedly　enhancing　the　thermal　stability　of　pristine　HPMC　hydrogels.　Sodium　sulfate　induces　a　Hofmeister　effect,　lowering　the　lower　critical　solution　temperature　to　32　°C　while　accelerating　phase　transition　rates　fivefold　(30　s　vs.　150　s).　Intriguingly,　small-sized　polydopamine　nanoparticles　simultaneously　enable　high　luminous　transmittance　of　66.9%　and　outstanding　anti-UV　capability.　Additionally,　the　smart　window　showcases　a　high　solar　modulation　(51.2%)　and　maintains　a　10.2　°C　temperature　reduction　versus　a　glass　window　during　all-day　modulation　applications.　The　design　strategy　is　effective,　opening　up　new　avenues　for　manufacturing　fast-response　and　durable　thermochromic　smart　windows　for　energy　savings　and　emission　reduction.　©　2025　The　Author(s).　Advanced　Materials　published　by　Wiley-VCH　GmbH.