Over the past few weeks I’ve been building a collection of free tools for developers and educators, hosted on my own server. No registration, no usage limits, no ads. Everything runs directly in the browser whenever possible, and when it needs a server, it runs on my Mac mini.

Here’s a summary of what’s available.

Spanish fake data generator

This one took the most effort and I think it has the most unique value.

Most fake data generators are designed for the English-speaking market: names like “John Doe”, addresses at “123 Main St” and American phone numbers. If you’re developing for Spain, that’s useless.

sergiocomeron.com/fake/ generates completely fictional but algorithmically valid data:

• NIF with the correct modulo 23 algorithm
• NIE with the initial letter substitution (X=0, Y=1, Z=2) and its check letter
• CIF (company tax ID) with the weighted sum algorithm
• Spanish IBAN with check digits calculated by modulo 97
• Credit cards that pass the Luhn algorithm
• Spanish names and surnames, addresses with real cities and provinces, mobile and landline phone numbers in Spanish format

It also has a free API with no registration:

1curl "https://sergiocomeron.com/api/fake/?tipo=persona&cantidad=5"

Useful for seeding test databases, generating fixtures in automated tests or creating demos with realistic data.

⚠️ All data is fictional and for development use only. It does not correspond to real people or accounts.

JSON formatter and validator

sergiocomeron.com/json/ — Paste any compressed or malformed JSON and it formats it instantly with syntax highlighting. If there’s an error, it shows the exact line and column. Supports 2-space, 4-space or tab indentation, and allows minification. Two parallel panels: input on the left, result on the right. Everything in the browser.

Hash calculator

sergiocomeron.com/hash/ — SHA-256, SHA-512, SHA-384, SHA-1 and MD5 from text or file. MD5 is implemented in pure JavaScript (Web Crypto API doesn’t support it). The file never leaves your browser.

Password generator

sergiocomeron.com/password/ — Passwords from 6 to 64 characters with full control over uppercase, lowercase, numbers and symbols. Option to exclude ambiguous characters (0, O, l, 1, I). Generates up to 10 at once. Uses crypto.getRandomValues() directly — real cryptographic randomness, no server involved.

QR generator

sergiocomeron.com/qr/ — Enter a URL or text and download the QR as PNG up to 1024×1024 pixels. No watermarks, no registration, with color and error correction level control.

Unix timestamp converter

sergiocomeron.com/timestamp/ — Shows the current Unix timestamp updating in real time. Converts in both directions (timestamp ↔ date), automatically detects whether the number is in seconds or milliseconds, and has a quick reference table with the epoch, the year 2038 problem and other relevant dates.

Lorem Ipsum generator

sergiocomeron.com/lorem/ — The differentiator here is the Spanish version. Most generators only offer classic Latin, which can be confusing in demos for Spanish-speaking clients. Generates paragraphs, sentences or words, with option to wrap in <p> tags.

Markdown to HTML converter

sergiocomeron.com/markdown/ — Editor with two panels: Markdown on the left, rendered result on the right, updating in real time. Supports full GFM syntax: tables, code blocks, quotes, images. Toggle between rendered preview and HTML source.

Secure secret sharing

sergiocomeron.com/secret/ — Share passwords or sensitive information with a link that works once and is destroyed when opened. The secret is encrypted with AES-256-GCM before storage; the decryption key only exists in the URL, never on the server.

All tools are available at sergiocomeron.com/links/. If you have suggestions or find a bug, contact me from the contact page.