Practical guides, how-tos and comparisons to get the most out of our free online tools.
The product paying the second-highest headline rate finishes last, and the reason is a tax change that took effect in January 2026. The three French savings vehicles scored on identical criteria: rate, tax, net return, real return, and what each one costs you in access.
Camille Laurent · 17 min read
The break-even is a division, and the number underneath it moves more with where you charge than with which country you live in. Electricity and fuel prices from 2025 and 2026, the arithmetic in full, and the point at which an electric car stops saving anything at all.
Marco Bianchi · 15 min read
Three ways to put the same car on the drive, priced over five years at the same interest rate. The monthly payments rank the options in exactly the reverse order of what they cost — and the gap turns out to be a single, computable number.
Marco Bianchi · 15 min read
You do not need a penalty clause. A European directive gives every business creditor a statutory interest rate and a fixed recovery sum, both due automatically, and a term in the contract trying to take them away is void or presumed unfair. Here are the current rates and what they produce on a real invoice.
Camille Laurent · 13 min read
RFC 8259 requires exactly three things to be escaped inside a JSON string. Everything else is optional. The one that actually breaks pipelines is a lone surrogate — legal in JSON text, impossible in UTF-8, and silently replaced the moment your data is written out.
Daniel Okonkwo · 13 min read
The same company, the same year, reads 1.02×, 1.52× or 2.56× depending on where rent is put and whether principal is grossed up for tax. Two of those pass a 1.25 covenant and one does not.
Camille Laurent · 17 min read
Overpaying earns exactly your mortgage rate, certainly and untaxed. An investment must therefore beat that rate divided by one minus the tax on its return — which at a 3.2 % mortgage means 4.57 % in a French ordinary account and 3.20 % inside the German savings allowance, before any reward for taking risk.
Camille Laurent · 15 min read
The usual advice is that a buy-back gets worse with age, because the price rises. The French scale is written to be actuarially neutral, so that is not quite what is happening — and once you see what actually moves the answer, the decision changes. Computed on the current parameters.
Camille Laurent · 14 min read
A missing quarter in France costs you twice over, through two separate mechanisms that most explanations mention only one of. A German point is a single arithmetic step and much easier to price. Both are computable, and the 2026 figures changed more than usual.
Camille Laurent · 14 min read
The smallest thing that is still a table is two lines: a header row and a delimiter row. Here is why the second one is mandatory in GitHub Flavored Markdown, where pipe tables do not exist at all, and what a generator does that hand-typing cannot.
Daniel Okonkwo · 13 min read
Put both on one axis — euros paid per kilowatt-hour a year of permanent saving — and the comparison becomes decidable. The same loft job costs 0.83 euros per kilowatt-hour a year in a 1965 house and 5.00 in a 2005 one, a factor of six. That, and not the age of the building by itself, is what inverts the verdict.
Marco Bianchi · 14 min read
The rule of thumb everyone repeats — one point of rate gap — is not a rule and gets the timing wrong. What decides it is how much interest you have not yet paid, and the three countries answer the cost side in three completely different ways. Here is the arithmetic, computed.
Camille Laurent · 13 min read