You buy a licence to use FastSheet, once, and you keep it. FastSheet is a viewer — it opens huge spreadsheets and never changes them. It is not Excel and does not replace it.
We sell the licence; Lemon Squeezy takes the money and handles the tax. If the app can't do what we said it does, ask for your money back within 14 days — that's the refund policy. Beyond the price you paid, we can't carry the risk of what you do with the numbers you read.
1. Who you are dealing with
LK Software is an independent software studio operated by Lê Mạnh Kha in Vietnam ("we", "us"). We are the author and licensor of the software.
Lemon Squeezy is our merchant of record. When you buy FastSheet, Lemon Squeezy is the party that processes your payment, issues your invoice, and collects and remits VAT or sales tax where it is due. The charge on your statement comes from them. The licence to use the software comes from us, on these terms.
By installing or using our software, you agree to these terms. If you don't agree, don't install it — and if you have already paid, see the refund policy.
2. What FastSheet is — and what it isn't
We would rather set this out here than let you discover it after paying.
- FastSheet is a read-only viewer for large
.xlsxand.csvfiles. It opens, displays, searches, filters, and summarises them, and can export a filtered view to a new file. It never writes back to your original file. - FastSheet is not a spreadsheet editor and is not a replacement for Excel. It does not edit cells, calculate formulas, make charts, or save changes to your workbook. If you need to change the file, you still need Excel.
- What "large" means. FastSheet is built for files that are heavy in megabytes and structural complexity — the workbooks that make Excel freeze. It is not a big-data tool. Note that a single
.xlsxworksheet can hold at most 1,048,576 rows; that is a limit of the file format itself, not something any viewer can lift. FastSheet also holds a file in memory, with a safety ceiling of 2,000,000 rows; if a file exceeds it, the app tells you the view was truncated rather than silently dropping rows. - Known display differences. Some cells render differently than Excel shows them — for example a cell formatted as
15%displays as0.15, and accounting negatives like(500)display as-500. The underlying values are correct; the presentation differs. Current known limitations are listed on the support page, and we keep that list honest.
Your right to a refund if the app doesn't do what we describe is set out in the refund policy, and this section is what "as described" means.
3. Your licence
When you buy FastSheet, we grant you a perpetual, non-exclusive, non-transferable licence to install and use the software.
- Buy once, keep it. It is a one-time purchase, not a subscription. There is nothing to renew and nothing to cancel. The version you bought does not stop working, ever — we cannot switch it off, and we would not build an app that let us.
- Personal or business use. You may use it for your own work, including at your job.
- How many machines. Your licence covers your own use on the computers you personally use, up to any activation limit shown at checkout. Reinstalling on a new machine is expected and fine.
- Updates. Updates within the version you bought are free. A future major version may be a separate purchase; if so, it will be priced and announced as such, not slipped into an update.
- Offline. Once activated, the app does not check in with anything. It works with no network, indefinitely.
3.1 What you may not do
- Resell, rent, sublicense, or redistribute the software or your licence key.
- Share your licence key publicly or with people outside your licence.
- Remove or alter copyright and ownership notices.
- Reverse-engineer, decompile, or disassemble the software, except to the extent that law expressly permits it despite this restriction.
4. PinRail (free software)
PinRail is provided free of charge, for personal and business use, with no licence fee and no purchase. Sections 5 to 8 apply to it too. Being free, it comes with no support commitment — though in practice we read every message. Optional donations are gratitude, not a contract, and buy no entitlement.
5. Installation and code signing
Our installers are not yet code-signed. Windows SmartScreen may therefore warn you about an "unknown publisher" the first time you run one. This is a statement about our certificate, not about the software. We say so on the support page too, because hiding it would be the wrong way to earn a first install. A signing certificate is on the way.
Download our software only from this website. We cannot vouch for a copy you got anywhere else.
6. Warranty, and its limits
We build carefully, we test on real files, and we publish what we measure. But the software is provided "as is", without warranties of any kind, express or implied, including implied warranties of merchantability, fitness for a particular purpose, and non-infringement. We do not warrant that it will be uninterrupted or error-free, or that it will open every file ever produced.
Nothing in these terms limits any rights you have as a consumer under the mandatory law of your own country, where such law says those rights cannot be excluded.
7. Check the numbers before you rely on them
FastSheet shows you what is in a file. It is a viewing tool, not an auditor. Do not treat what it displays as verified accounting, financial, tax, or legal fact — for any decision that matters, verify against the source. This matters most where display differs from Excel (see §2), and in one known case, statistics on CSV files that use a comma as the decimal separator can be miscalculated. That case is documented on the support page rather than left for you to discover.
8. Limitation of liability
To the fullest extent permitted by law, we are not liable for indirect, incidental, special, consequential, or punitive damages, or for lost profits, lost revenue, lost data, or business interruption, arising out of or related to the software — even if we were told such damage was possible.
Our total liability to you for any claim relating to the software is limited to the amount you actually paid for it in the twelve months before the claim. For PinRail, which is free, that amount is zero. This limit does not apply to liability that cannot lawfully be limited, such as our own fraud.
9. Price, payment, and tax
FastSheet is USD 29, one time. Prices are shown at checkout and may change for future purchases; a change never affects a licence already bought.
Lemon Squeezy adds VAT or sales tax where your country requires it, and shows it before you pay. They issue the invoice. If you need a tax invoice or a VAT number on it, their checkout is where to enter it, and their receipt is the document your accountant wants.
10. Refunds
Set out in full in the refund policy, which forms part of these terms.
11. Termination
Your licence lasts as long as you keep to these terms. If you materially breach them — for example by redistributing the software or your key — the licence ends, and you must stop using and uninstall the software. You may stop using it at any time; uninstalling is enough, and there is no account to close.
12. Governing law
These terms are governed by the laws of Vietnam, and the courts of Vietnam have jurisdiction over disputes arising from them. If you are a consumer, this does not deprive you of the protection of the mandatory law of your country of residence.
13. Changes to these terms
We may update these terms for future sales; the version in force when you bought is the one that governs your purchase. Material changes will be dated at the top of this page.
14. Contact
LK Software · Vietnam · SUPPORT_EMAIL_PLACEHOLDER
See also: Privacy Policy · Refund Policy · Support