The usual Palo Alto diagnosis
On the city's older decks the sequence is predictable: post bolts lose their bite as the rim joist cycles through wet and dry seasons, then the post base collects water at the deck surface and softens. If tightening hasn't helped, the wood the bolts clamp is the problem — and catching a softening rim joist early is the difference between a local repair and rebuilding the deck edge.
Next step
Each loose post at its base connection, the run from the side, and — if the post rocks — a short video of the movement. Send through the form for a range.
Railing mechanics: see the service page. City rules: see the Palo Alto page.