EasyCard

EasyCard is absolutely worth getting for a 4-day trip to Taipei. It is Taiwan’s premier contactless smartcard, and it will save you both time and hassle on almost every transit ride you take.
Instead of lining up at ticket machines to buy individual plastic tokens before every single ride, you simply tap the card at the gate to enter and exit.

Why It is Worth It for a 4-Day Trip
Seamless Transit: It works on the entire Taipei Metro (MRT), the Taoyuan Airport MRT, all city buses, and even the local TRA trains if you take a day trip to places like Jiufen or Shifen.
Convenience Store Currency: You can use it like cash at 7-Eleven, FamilyMart, Hi-Life, and OK Mart. It is perfect for buying snacks, water, or coffee without dealing with heavy metal coins.
Other Uses: You can use it to pay for the Maokong Gondola, YouBike public bicycle rentals, and admissions to top sights like the Taipei Zoo.

The Math: Cost vs. Benefit
Card Cost: A standard EasyCard costs NT$100 (about USD $3). This is a non-refundable registration deposit for the physical card itself.
The Verdict: Even though you don’t get the NT$100 back, the sheer convenience of skipping lines at every station, not fumbling for exact change on city buses (which don’t give change), and easily buying items at convenience stores makes it well worth the small cost for 4 days.

How and Where to Buy It
At the Airport: After you land and withdraw your cash, you can buy an EasyCard directly at the Taoyuan Airport MRT service counters or from the automated ticket machines right outside the MRT gates.
At Convenience Stores: You can also walk into any airport 7-Eleven or FamilyMart and buy one at the counter. Convenience stores often sell cards featuring cute, limited-edition designs (like anime characters or local food shapes).
Adding Funds: When you buy the card, it has a NT$0 balance. You will need to load cash onto it immediately. For a 4-day trip, starting with a top-up of NT$500 to NT$800 is usually plenty for transit and light snacking. You can easily add more cash later at any MRT station machine or convenience store counter.

EasyCard refund
You can get the remaining balance refunded, but there are a few important rules you should know before doing so.
While the cash balance you top up onto the card is fully refundable, the initial NT$100 card purchase fee is strictly non-refundable. Additionally, once you request a refund, your card will be permanently deactivated and cannot be used again.

Where and How to Get a Refund:
Where to go: You can request a refund at any Taipei MRT station information counter or right at the Taoyuan Airport MRT station service booth before you clear security for your flight home.
The Process: Simply hand your card to the staff at the ticketing window and tell them you want a refund. They will scan the card, calculate the remaining balance, and hand you the amount in cash.
The Cost: There is a NT$20 processing fee to terminate the card.
Cash Limit: You can get an immediate cash refund for balances up to NT$1,000. Anything higher requires a bank transfer, which is incredibly difficult for international tourists.

The Smarter Local Alternative: Clear the Balance
Because the NT$100 card fee is lost and a processing fee might apply, most travelers on travel forums like Facebook recommend not refunding the card at all.
Instead, do what the locals do on your final day: walk into an airport convenience store (like 7-Eleven or FamilyMart) and spend your exact remaining balance on souvenirs, snacks, or milk tea. If your purchase total is higher than what is left on the card, you can simply tap the card to drain it to zero and pay the remaining difference in cash.
By doing this, you get to keep the physical card as a souvenir, and it remains valid for several years in case you ever return to Taiwan.