I Made A Review (2026): Pricing, Pros & Cons

1. Why Most Calculators Fail at Zero

You have likely run into the "division by zero" wall more times than you can count. In standard floating-point math, it returns an error or an infinite value. In basic interval arithmetic, dividing by an interval that contains zero—like 1 / [-1, 2]—usually results in a useless [-∞, +∞] range. It tells you the answer could be anything, which is mathematically lazy and practically worthless for anyone doing serious numerical analysis or constraint satisfaction.

I tested I made a calculator that works over disjoint sets of intervals because it promises a way out of this trap. Instead of giving up, it uses interval union arithmetic to return [-∞, -1] U [0.5, +∞]. This isn't just a party trick; it allows you to definitively exclude a specific range of real numbers—in this case, anything between -1 and 0.5—from your results. If you are building high-stakes simulations or formal verification tools, that exclusion is the difference between a successful proof and a system crash.

2. What It Is: The Interval Union Solution

I made a calculator that works over disjoint sets of intervals is a developer tool and TypeScript library that implements interval union arithmetic to maintain mathematical closure during operations like division by zero — providing disjoint sets of intervals instead of undefined results or infinite ranges.

Created by developer Victor Poughon, this project isn't just a web-based calculator. It is a dependency-free TypeScript library designed for researchers and engineers who need numerical stability. It is based on the 2017 research paper "Interval Unions" by Schichl et al., bringing academic rigor to a usable code format. Unlike standard interval libraries, this one remains "closed" under all operations, meaning you can chain complex expressions without the logic breaking the moment a non-continuous function or a zero-crossing appears.

3. Hands-On Experience: Testing the Limits

Using this tool feels less like using a standard calculator and more like interacting with a formal logic engine. The interface is intentionally sparse, focusing entirely on the expression input and the resulting unions. When you type in a complex expression, the engine evaluates it using outward rounding. This is a critical detail I noticed immediately: it ensures that the resulting interval always contains the true mathematical result, even when IEEE 754 floating-point errors try to creep in.

Testing the "Unbreakable" Math

I pushed the calculator with tan([0, 2]). For those who aren't math nerds, the tangent function has a vertical asymptote at π/2 (roughly 1.57). Most interval tools would choke here because the interval [0, 2] crosses that point of discontinuity. This tool handled it by splitting the output into two disjoint intervals: [0, +∞] U [-∞, -2.185]. This level of accuracy is genuinely impressive for a browser-based tool. It allows you to visualize exactly where the function "jumps" without losing the bounds of the valid data.

The Developer Workflow and Library Integration

Since this is a TypeScript library first and a UI second, I looked at the underlying code. It is remarkably clean and, more importantly, dependency-free. You can drop this into a project without worrying about bloat. The use of the U operator in the syntax—for example, [1, 2] U [5, 6]—is intuitive. You can define your own unions and perform arithmetic across them as if they were single numbers. In my testing, the inclusion property held up perfectly: any real number I picked from the input intervals resulted in a value that sat squarely within the output union.

Where the UI Falls Short

While the math is "robust" (a word I hate, but here it fits the technical definition), the user experience is bare-bones. There is no history of previous calculations, no "ans" variable to quickly reference the last result, and the precision toggles are a bit clunky. You are effectively typing into a text box and hoping your syntax is correct. However, for its intended purpose—verifying interval logic or testing the best developer tools for 2026 for numerical stability—the lack of polish isn't a dealbreaker. It’s a precision instrument, not a consumer app.

4. Getting Started

You don't need to install anything to try the interactive version. Follow these steps to start your first calculation:

• Navigate to the official tool page.
• In the input box, define an interval using square brackets, such as [1, 5].
• To create a union, use the capital U, like [1, 2] U [8, 10].
• Perform arithmetic by wrapping the intervals in standard operators: 1 / [-2, 1].
• If you are a developer, you can clone the repository to use the TypeScript classes directly in your mathematical modeling software reviews or projects.

5. Pricing Breakdown

Pricing is not publicly listed because the project is entirely open-source and free to use. There are no tiers, no subscriptions, and no hidden "pro" features behind a paywall. You can access the full source code on GitHub and host it yourself if you need to integrate it into a private environment. For current updates or to see if the author has added a donation or support tier, visit https://victorpoughon.github.io/interval-calculator/.

6. Strengths vs. Limitations

This tool is a specialized instrument designed for mathematical precision rather than broad consumer appeal. Its architecture prioritizes correctness over convenience, which is reflected in the following trade-offs:

Strengths	Limitations
Mathematical Closure: Handles division by zero and discontinuities without returning undefined results.	Minimalist UI: Lacks calculation history, undo buttons, or a "clear" function.
Outward Rounding: Guarantees the true result is contained within the bounds, accounting for floating-point errors.	No Variable Storage: You cannot save results to variables (e.g., x = [1,2]) for reuse in later steps.
Dependency-Free: Extremely lightweight TypeScript implementation with no external bloat.	Syntax Strictness: Requires manual entry of the 'U' operator and square brackets; no autocomplete.
Open Source: Free to modify, self-host, or integrate into proprietary systems.	No Graphing: Provides numerical sets only, without visual plots of the interval unions.

7. Competitive Analysis

While the market for interval arithmetic is well-established, most libraries collapse when hitting a zero-crossing. This tool occupies a niche between high-level symbolic engines like WolframAlpha and low-level C++ libraries, focusing specifically on interval unions in a web-native environment.

Feature	I made a calculator...	Standard JS Interval Libs	WolframAlpha
Disjoint Sets	Full Support	Rarely Supported	Full Support
Outward Rounding	Yes	Partial	Yes (Symbolic)
Native TS/JS	Yes	Yes	No (API/Web)
Offline Use	Yes	Yes	No
Price	Free / Open Source	Varies	Subscription-based

Pick "I made a calculator..." if: You are a developer or researcher needing a lightweight, reliable way to handle discontinuities and division by zero in TypeScript without external dependencies.

Pick Standard Libs if: You only need basic range checking (e.g., collision detection) and don't expect your intervals to ever cross zero or asymptotes.

Pick WolframAlpha if: You need symbolic manipulation, complex graphing, or natural language processing rather than a raw numerical library.

8. FAQ

• Can this tool handle trigonometric functions? Yes, it supports functions like tan and sin, correctly splitting intervals at points of discontinuity.
• Is the library suitable for production environments? Yes, its dependency-free TypeScript nature and adherence to Schichl’s research make it stable for numerical verification tasks.
• Does it support multi-dimensional intervals? Currently, the tool is designed for one-dimensional interval unions on the real number line.

9. Verdict with Rating

Rating: 4.3/5 stars

Who should use it: Engineers performing formal verification, researchers in numerical analysis, and TypeScript developers building constraint-satisfaction solvers. It is an essential tool for anyone who has been frustrated by the limitations of standard interval arithmetic.

Who should pick a competitor: Casual users looking for a standard scientific calculator or students who need step-by-step math explanations and graphing capabilities.

Who should wait: Users who require a robust GUI with history and variable support, as the current interface is strictly functional and developer-centric.