You can technically get by in Japan without a Japanese bank account. For those who are here on short-term visas, or who plan to move frequently from city to city, it’s perfectly possible to live and work in Japan without one. However, if you want to work a full-time job, rent an apartment, join social activities, or enroll your children in school, you’ll almost certainly need to make an account. Following is an overview on what you’ll need to open an account, some common problems foreigners encounter, and what banks will work best for your needs. If you don’t have a bank account . . . The “chicken-and-egg problem” is what many foreigners call it—that strange bureaucratic trap you encounter when moving to Japan. You need a local phone number to get an apartment, but you need a registered address to get a bank account, and you need a bank account to get a local phone number! Luckily, there is an order of operations that can get you all three as fast as possible. But let’s say you haven’t decided where you want to live yet, or there’s some other reason for delay. Can you get by in Japan without an account? Strangely enough, it’s not that difficult, thanks to Japan’s cash-based society. Getting paid Direct deposit is more common now, and most companies will also ask you to make an account with a specific bank to receive your paycheck. Nonetheless, they cannot require you to make an account with that bank. You are within your rights to insist on being paid to the account of your choice. Getting cash Be aware that Japan has two methods of getting cash from a machine: ATMs, which function generally like ATMs around the world, and cash machines, which are usually located in banks and are only usable with that bank’s cash card. For example, if you go into Mitsui Sumitomo and have a cash card for some other bank, you will not be able to use it. Many ATMs found at convenience stores, as well as Japan Post Bank ATMs, will allow you to withdraw yen from your foreign accounts. Of the various convenience store options, 7-Eleven ATMs are your best bet. There are some limitations: Depending on the ATM, additional fees may be charged Many ATMs can’t check your foreign account’s balance The single transaction withdrawal limit may be reduced—at Japan Post Bank ATMs, you can’t withdraw more than 50,000 yen from a foreign account at one time 7-Eleven ATMs do not allow you to freely select an amount to withdraw and instead require you to pick from options starting from 10,000 yen and up Using your foreign card In addition, most stores that accept credit or debit cards will also be able to process foreign-issued cards—at least, I’ve never had mine rejected. If the store is not large or is not part of a national chain, however, the odds of them not being able to process your card are higher. Additionally, some stores may not be able to support chips, so if your card does not have a magnetic stripe, you would be unable to use it. As a side note, one of the services that does not permit foreign credit cards is the one you’d least expect—Disneyland. If you want to purchase park tickets online, the website theoretically accepts most foreign cards, yet very few seem to actually work. Personally I got around this problem by using Klook, a third-party app that had no difficulty processing my credit card, and delivered my digital tickets without issue. Finding housing Finally, share-houses and other short-term, foreigner-friendly rental accommodations don’t require a Japanese bank account to rent. These often come furnished, may include utilities, and can be rented without the hassle of a deposit or key money. Of course, they will cost more overall than long-term housing, but they’re good options for those without a Japanese account. But you should make a bank account As you can see, it’s possible to live in Japan without a Japanese account, at least for a while. But it’s not convenient, and the longer you live in Japan, the more inconvenient it becomes. Renting Renting your own apartment with a long-term lease will almost certainly require a Japanese bank account. In this case, having a Japanese bank account and phone number is the bare minimum; they will also want to see your residency status, employment contract or income statement, and either guarantors or the endorsement of a guarantor company. In addition, while you can pay most utility bills with cash at a convenience store, it’s becoming more and more convenient to set up automatic withdrawal, with some companies attempting to discourage convenience store payments by applying a service fee for the paper bill. Automatic withdrawals also mean you’re less likely to miss a payment and have your gas turned off without warning, as happened to me! Employment Your employer will also want you to make a bank account, as almost all big businesses prefer direct deposits. Government benefits The government, at a certain point, requires you to have a local account. It’s how you can expect to receive your tax refund and any social benefits you may be entitled to, such as the child support allowance (jidou teate, 児童手当). Japanese society Aside from the basics of life, many social clubs, activities, and schools require participants to have bank accounts. This will depend somewhat on where you live. In Tokyo, my husband’s taiko club insisted that he set up monthly debits from a Japanese account in order to participate. My children’s public elementary school required us to make an entirely new account with their preferred bank, so that they could withdraw lunch fees. By contrast, in our new small town in Kansai, the children’s karate and ballet classes are cash-only. The school did ask us to make a new account at a regional bank for lunch fees, but when we were unsuccessful—a point I’ll explore below—they were fine with collecting the payments in cash. In short, it’s better to bite the bullet and make the account. The actual difficulty of doing so will depend on which bank you choose. The kinds of banks in Japan There are of course all kinds of banks in Japan, from online banks to large national institutions. From the immigrant’s point of view, however, there are several distinct categories. Japan Post Bank The Japan Post Bank (Yuucho Ginkou, ゆうちょ銀行) deserves a category of its own. Unlike other banks in Japan, the Japan Post Bank does not require six months residency or an employment contract in Japan to open an account. You must, however, have at least three months remaining on your residence card when you apply. In addition, if you have less than six months residency and no employment contract, your account will be treated as a non-resident account with limited services. There are branches all over Japan wherever a post office is; you can also open an account online. Conventional foreigner-friendly banks Several banks in Japan are well known for being foreigner-friendly and providing some English services. SMBC Trust Bank Prestia and SBI Shinsei Bank are the usual recommendations in this category. Both offer English-language online banking, and English support via chat. Online banks You can also select a bank that operates purely online (netto ginkou, ネット銀行). For simple bank procedures, such as acquiring a debit card and depositing your paycheck, these don’t operate much differently from conventional banks. Popular choices include: PayPay, which operates a thriving cashless payment service Sony Bank, which has 90,000 partner ATMs in Japan Seven Bank, the official online bank of 7-Eleven and has ATMs in every branch Japanese-speaking banks Aside from convenience, there’s really nothing stopping you from banking with any bank in Japan. You should be able to make an appointment at any branch and request their help in opening an account. Granted, this approach requires time, patience, possibly multiple appointments, and—if you don’t speak Japanese—a lot of translation. Nonetheless it can be done, and will probably even be necessary at one point or another, since jobs, schools, and activities in Japan may ask you to work with their preferred bank. What you’ll need to apply Typically, this is what you’ll need to open an account with a bank: Your residence card. This is always required. A second form of ID. This could include your My Number card, your student ID, your Residence Certificate (住民票, juuminhyo), or a utility bill or other document with your full name in katakana. The exact specifications for a second form of ID differ from bank to bank, so check their instructions carefully. An employment contract and/or Employee ID. For most banks, if you want to open an account before you’ve lived in the country for six months, you will need to provide proof of employment. A local phone number Do I need a hanko? A hanko (判子, also called an inkan 印鑑) is a stamp which, on many Japanese documents, serves as your official signature. Do you absolutely need to have one to open an account? Not necessarily. Some banks, such as Japan Post Bank, will permit you to start banking with only your signature. Should you buy and use one anyway? Yes, for several good reasons: You may need it later for more advanced procedures, such as renting an apartment, getting a loan, or car registration. If your signature doesn’t match exactly when you’re submitting paperwork in the future, your bank may reject it. A hanko will remain the same, as long as it is not damaged. If you damage or lose your hanko, the bank will require you to re-register the imprint so that they have a current copy on file. If you sign up for a bank account with your signature, but later acquire and use a hanko, this can lead to confusion with your bank. Again, a Japanese bank will reject paperwork with any inconsistencies. This may not seem like a hard thing to keep straight, but if and when you have multiple accounts in Japan, remembering which requires your signature and which requires hanko can be a hassle. Why not? Hanko are not that expensive, they make great souvenirs, and they’re an easy way to integrate. My own hanko has my surname in katakana, and receives a lot of interest from Japanese people due to its unique appearance. If you’re intimidated by the process of buying a hanko in person, you can order one online. I used Google Translate to buy mine at Shibuya Stamp Shop, but there are English websites available as well. Be careful not to buy a hanko that is self-stamping (such as a shachihata), as many banks will refuse to accept them. Additionally, you should make sure that you carefully store the hanko you use for bank accounts and use it only for bank accounts. It is fine to use one hanko for multiple bank accounts. People commonly have several hanko, each for different levels of tasks; you don’t want to be stamping delivery slips or kids’ homework with the same security device you use to control your finances! U.S. citizen requirements U.S. citizens and green card holders will require a few more documents, thanks to the Foreign Account Tax Compliance Act (FATCA). If you’re opening an account in person, you should bring your passport and social security card with you. If you’re opening the account online, expect to fill out additional forms to establish your TIN (Taxpayer Identification Number). Usually these forms will be requested by mail, which delays the so-called “online application” process considerably. For U.S. citizens and green card holders, it’s faster to apply for an account in person. Should I apply online? Quite a few banks now claim to offer online applications in English, to ease account opening procedures. But what is meant by an “online application” can differ hugely. By smartphone is best First, if you want to apply online, it’s best to have a smartphone with a domestic SIM. Smartphones are the main way consumers access the internet in Japan, so many solutions are built smartphone-first. You can often save several steps by using a smartphone. For example, if you apply via smartphone with SMBC Trust Bank Prestia, you have the option to take a selfie as one form of ID, which means you only need your residence card. Do note that the facial ID process can be finicky for these systems, and may reject your photo. If you use a computer or tablet, however, the bank requires two forms of ID. Seven Bank, as an online bank, also strongly prefers customers to use a smartphone; those who don’t have one can use a Debit Card and conduct transactions from its ATMs, but won’t be able to use their Direct Banking Service. Is it really online? “Applying online” isn’t always as simple as it sounds. Japan Post Bank and Sony Bank both allow users to make an account via the bank’s app, a process that they claim takes around 30 minutes. But Shinsei’s online application barely qualifies as such. While you do fill out the initial form on the website, it’s only so you can receive a printed application form in the mail around one week later. You’ll then have to send back copies of your IDs to the bank via mail, for an additional 7-10 business days of processing—at which point, you might be better served by visiting a branch with Google Translate. Online-only banks often have similar processing times for foreigners, but with an additional down side: since they’re online-only, there is no option to visit a local branch and hammer everything out in one go! These estimated application times also depend on everything going smoothly via the bank’s app or website, which is not guaranteed. Modern banks often rely on relatively new MyNumber card integrations, or “AI” facial/document recognition, and bugs are unfortunately common. Common problems Forewarned is forearmed, and in that spirit, here are some of the most common issues experienced by foreigners banking in Japan. Technical difficulties Personally I bank with Japan Post Bank, and am very happy with the service I receive—-except when I need to try and set up a new direct withdrawal online. For whatever reason, I’ve found that trying to access the forms via Chrome causes all sorts of problems. Switch to Safari, though, and suddenly everything works. Using VPNs, adblockers, or other common security extensions can also frequently cause issues with financial sites in Japan. Name issues If you take away one important thing from this article, let it be this. From the beginning, choose the Japanese version of your name and keep it consistent. It’s a given that if you do not have a Japanese name, you will need to spell it out in katakana. However, for many names there are several accepted katakana variations. For example, I prefer to spell my surname Callahan as カラハン (Karahan), but it was spelled (without my input) as キャラハン (Kyarahan) on my health insurance card. Fortunately I didn’t run into any issues and was able to change it later. However, that would have caused issues with opening a bank account, if I’d attempted to use my health insurance card as a secondary form of ID. Long names and middle names will also cause problems—unfortunately, these are mostly unavoidable. There frequently isn’t enough space in a form to write your name properly, either in the Roman alphabet or in katakana. You might be tempted to leave out your middle name whenever possible, but you risk your application not being accepted because it doesn’t match your full legal name. For me personally, a long legal name has been only a minor inconvenience. However, for my Sri Lankan neighbor, her long name created so many problems that she was unable to open an account at our local bank. Although she is a permanent resident and speaks Japanese fluently, even after three separate trips to the bank, she was still unable to open the account. Banks will also unfortunately have different recommendations in the event that your full name does not fit their paper or electronic application; some will ask that you fill in as much as possible and truncate, while others may concede and allow only your first and last names. Still other banks may require you to use your English name and not accept a primary katakana rendering. These mismatches can cause issues when attempting to connect accounts in the future, and those can usually only be solved with human help—perhaps a reason to consider banking at an institution that has physical branches. Kanji difficulties Several times I’ve been asked to create a new account with a regional bank that didn’t offer service in English. Both times, I was asked by bank employees to fill out several forms with my address written in kanji. Best practice, of course, would be to have already memorized my own address in kanji. In reality, I ended up copying it from the tiny writing on the back of my residence card. At the first bank, the kind employees carefully showed me how to write some of the more complicated kanji. At the second, I was mostly left to my own devices, and the subsequent scrawl caused my application to be rejected; they asked me to come back with someone who spoke, and wrote, Japanese. If you do need to open an account at a Japanese-speaking bank, try keeping a copy of your address in your phone, or even printing out the kanji version in large characters that are easier to copy. Of course, if you have a Japanese-writing friend who is willing to accompany you that day, that will also speed things along. I’ll add that the bank that rejected me was the same bank that my neighbor applied to three times. I wouldn’t describe my visit there as an ordinary banking experience in Japan; this particular branch is clearly unwilling to assist or accommodate foreign residents. A cash card is not a debit card Perhaps this isn’t a widespread misunderstanding, but it caught me by surprise: most banks provide only cash cards by default, and debit cards are opt-in. A cash card is not a debit card—it is good only for pulling cash out of a cash machine or ATM. Some banks, such as Prestia and Sony, do give you a debit card straight away. Others, such as Japan Post Bank, require a subsequent application for a debit card once the account is open. You can distinguish a cash card from a debit card by looking for a network logo such as Visa, Mastercard, or JCB. If it does not have one, it’s likely a cash card. Holidays and ATM times If you live or work near convenience stores, you shouldn’t have much problem withdrawing cash whenever you want. However, you should still keep an eye out for ATM working hours or your bank’s maintenance hours. For example, many ATMs are unusable over a portion of the New Year or Golden Week. Japan Post Bank shuts down completely for part of Golden Week—a shutdown that includes ATMs, online services, the smartphone app, and even your debit card! You should also keep an eye on time-sensitive withdrawal fees. Many ATMs will display a screen that shows one withdrawal fee for business hours, and another for early morning or late-night transactions. The difference is fairly small—a business-hour withdrawal may cost 110 yen, as opposed to a late-night withdrawal at 220 yen—but if you’re cost-conscious, it’s good to take note. Sending and receiving money internationally The cost of sending and receiving money internationally adds up quickly. Not only do Japanese banks often charge steep fees for currency conversion and wiring, but there’s yet more paperwork involved. If you enjoy a prestigious bank account, such as the Sony Bank and Shinsei Platinum accounts, then one of the perks is lowered or waived fees for international transfers. If you don’t, then an online transfer service like Wise is certainly faster and frequently cheaper. If you are interested in moving large amounts of money and want to avoid fees as much as possible, here’s a detailed breakdown of the average transfer rates for various institutions and accounts. Frequently-recommended banks Following are some of the banks most often recommended by other immigrants, with a brief overview of their pros and cons. Japan Post Bank Japan Post Bank is one of the easiest banks to open an account with when you first arrive in Japan. Pros Doesn’t require six months residency or an employment contract to open an account Branches all over Japan in the post offices Can open an account and check your virtual bankbook via apps No monthly maintenance fees Cons Service is mostly in Japanese Services may be limited and fees may be high during the first six months if you do not have an employment contract Have to apply separately for a debit or bank card Access to ATMs on post office grounds is limited to the hours for that branch, which can be inconsistent High fees for international transfers SBI Shinsei Bank Shinsei is a good choice for those who want some service in English, and who intend to send and receive money internationally. Pros English Internet banking and online service Foreign currency accounts with high interest rates Free ATM withdrawals up to five times a month If you have a higher-level account (Diamond, Platinum, Gold, or Silver) you can receive foreign currency remittances for free Cons The “online” application procedure is really more by mail Initially only given a cash card Standard accounts are charged 2,200 yen per remittance SMBC Trust Bank Prestia Prestia is ideal for those who want a full-service bank that offers a travel-friendly debit card. Pros English-language bank app, online service, and assistance for housing loans, investment, etc. If you apply for an account via the app, you only need your residence card as a form of ID (assuming you meet the six-month residency requirement) Upon opening an account, automatically get both a yen account and a foreign currency account Immediately receive a GLOBAL PASS Visa debit card that can be used domestically and overseas Cons Monthly maintenance fee of 2,200 yen unless you keep a minimum balance of 500,000 yen or meet other requirements Easily confused with SMBC Bank, but the services and branches are not interchangeable Sony Bank For those who’d prefer an online bank, Sony Bank offers another international-friendly debit card and a comprehensive rewards system. Pros Automatically get the Sony Bank WALLET cash card, which can be used internationally Has Club S, a three-tier rewards system based on the balance of your yen and foreign currency accounts. Platinum members can get perks such as 2% cashback, unlimited free cash withdrawals, waived transfer and remittance fees, etc. Cons Only online banking is available in English (the app is in Japanese) As an online bank it has no physical branch to visit Special note: the Rakuten credit card Rakuten also has an online bank. While this is less often suggested as a bank for new immigrants, it is one of the few places foreigners can easily apply for a credit card. Conclusion Like most bureaucratic processes in Japan, opening an account can take quite a bit of time and paperwork, but is ultimately doable, not to mention beneficial in the long run. To recap: If you intend to live and work in Japan for more than a few months, you should open a local bank account. Japan Post Bank doesn’t require six months residency or employment to open an account, as other banks do. Banks such as SBI Shinsei, SMBC Trust Bank Prestia, and Sony Bank have a reputation for being foreigner-friendly; however, with proper preparation, you can have an account at any bank in Japan. The greatest difficulties in banking tend to be name-related. You can avoid most of them by keeping your legal name and its katakana spelling consistent from the beginning, as well as obtaining a hanko before opening the account. U.S. citizens and green card holders should expect more paperwork related to FATCA. Judging by these banks’ English-language sites, they’re pushing non-Japanese-speaking customers towards applying online or via mail rather than visiting their branches. However, if you’re a U.S. citizen, or just don’t want to download yet another app, don’t be afraid to go in person. With the exception of one local bank, I’ve consistently had positive experiences with bank personnel—they’ve often gone above and beyond to help me, despite the language barrier. So long as you’re patient with the process, and do your research on bank requirements, then opening an account will swiftly be one more item checked off that moving-to-Japan list.

Back in 2018, I wrote lethain/systems as a domain-specific language for writing runnable systems models, and introduced it with this blog post modeling a hiring funnel. While it’s far from a perfect system, I’ve gotten a lot of value out of it over the last seven years, because it allows me to maintain systems models in version control. As I’ve been playing with writing Model Context Protocol (MCP) servers, one I’ve been thinking about frequently is one to help writing systems syntax, and I finally put that together in the lethain/systems-mcp repository. More detailed installation and usage instructions are in the GitHub repository, so I’ll just share a couple of screenshots and comments here. Starting with the load_systems_documentation tool which loads a copy of lethain/systems/README.md and a file with example systems into the context window. The biggest challenge of properly writing DSLs with an LLM is providing enough in-context learning (ICL) examples, and I think the idea of providing tools that are specifically designed to provide that context is a very interesting idea. Eventually I imagine there will be generalized tools for this, e.g. a search index of the best ICL examples for a wide variety of DSLs. Until then, my guess is that this sort of tool is particularly valuable. The second tool is run_systems_model which passes the DSL (and an optional parameter for number of rounds) to the tool and then returns the result. I experimented with interface design here, initially trying to return a rendered chart of the results, but ultimately even multi-modal models are just much better at working with text than with images. This meant that I had the best results returning JSON of the results and then having the LLM build a tool for interacting with the results. Altogether, a fun little experiment, and another confirmation in my mind that the most interesting part of designing MCPs today is deciding where to introduce and eliminate complexity from the LLM. Introduce too little and the tool lacks power; eliminate too little and the combination rarely works.

Merkle Trees in the real world

Hey peoples! Tonight, some meta-words. As you know I am fascinated by compilers and language implementations, and I just want to know all the things and implement all the fun stuff: intermediate representations, flow-sensitive source-to-source optimization passes, register allocation, instruction selection, garbage collection, all of that. It started long ago with a combination of curiosity and a hubris to satisfy that curiosity. The usual way to slake such a thirst is structured higher education followed by industry apprenticeship, but for whatever reason my path sent me through a nuclear engineering bachelor’s program instead of computer science, and continuing that path was so distasteful that I noped out all the way to rural Namibia for a couple years. Fast-forward, after 20 years in the programming industry, and having picked up some language implementation experience, a few years ago I returned to garbage collection. I have a good level of language implementation chops but never wrote a memory manager, and Guile’s performance was limited by its use of the Boehm collector. I had been on the lookout for something that could help, and when I learned of it seemed to me that the only thing missing was an appropriate implementation for Guile, and hey I could do that!Immix I started with the idea of an -style interface to a memory manager that was abstract enough to be implemented by a variety of different collection algorithms. This kind of abstraction is important, because in this domain it’s easy to convince oneself that a given algorithm is amazing, just based on vibes; to stay grounded, I find I always need to compare what I am doing to some fixed point of reference. This GC implementation effort grew into , but as it did so a funny thing happened: the as a direct replacement for the Boehm collector maintained mark bits in a side table, which I realized was a suitable substrate for Immix-inspired bump-pointer allocation into holes. I ended up building on that to develop an Immix collector, but without lines: instead each granule of allocation (16 bytes for a 64-bit system) is its own line.MMTkWhippetmark-sweep collector that I prototyped The is funny, because it defines itself as a new class of collector, fundamentally different from the three other fundamental algorithms (mark-sweep, mark-compact, and evacuation). Immix’s are blocks (64kB coarse-grained heap divisions) and lines (128B “fine-grained” divisions); the innovation (for me) is the discipline by which one can potentially defragment a block without a second pass over the heap, while also allowing for bump-pointer allocation. See the papers for the deets!Immix papermark-regionregionsoptimistic evacuation However what, really, are the regions referred to by ? If they are blocks, then the concept is trivial: everyone has a block-structured heap these days. If they are spans of lines, well, how does one choose a line size? As I understand it, Immix’s choice of 128 bytes was to be fine-grained enough to not lose too much space to fragmentation, while also being coarse enough to be eagerly swept during the GC pause.mark-region This constraint was odd, to me; all of the mark-sweep systems I have ever dealt with have had lazy or concurrent sweeping, so the lower bound on the line size to me had little meaning. Indeed, as one reads papers in this domain, it is hard to know the real from the rhetorical; the review process prizes novelty over nuance. Anyway. What if we cranked the precision dial to 16 instead, and had a line per granule? That was the process that led me to Nofl. It is a space in a collector that came from mark-sweep with a side table, but instead uses the side table for bump-pointer allocation. Or you could see it as an Immix whose line size is 16 bytes; it’s certainly easier to explain it that way, and that’s the tack I took in a .recent paper submission to ISMM’25 Wait what! I have a fine job in industry and a blog, why write a paper? Gosh I have meditated on this for a long time and the answers are very silly. Firstly, one of my language communities is Scheme, which was a research hotbed some 20-25 years ago, which means many practitioners—people I would be pleased to call peers—came up through the PhD factories and published many interesting results in academic venues. These are the folks I like to hang out with! This is also what academic conferences are, chances to shoot the shit with far-flung fellows. In Scheme this is fine, my work on Guile is enough to pay the intellectual cover charge, but I need more, and in the field of GC I am not a proven player. So I did an atypical thing, which is to cosplay at being an independent researcher without having first been a dependent researcher, and just solo-submit a paper. Kids: if you see yourself here, just go get a doctorate. It is not easy but I can only think it is a much more direct path to goal. And the result? Well, friends, it is this blog post :) I got the usual assortment of review feedback, from the very sympathetic to the less so, but ultimately people were confused by leading with a comparison to Immix but ending without an evaluation against Immix. This is fair and the paper does not mention that, you know, I don’t have an Immix lying around. To my eyes it was a good paper, an , but, you know, just a try. I’ll try again sometime.80% paper In the meantime, I am driving towards getting Whippet into Guile. I am hoping that sometime next week I will have excised all the uses of the BDW (Boehm GC) API in Guile, which will finally allow for testing Nofl in more than a laboratory environment. Onwards and upwards! whippet regions? paper??!?