What counts as a developer tool?

Any small utility that helps debug, format, validate, or generate code-adjacent content. The category covers token decoders, expression testers, schedule parsers, format validators, network calculators, permission helpers, and credential generators.

Is it safe to paste a real JWT into the decoder?

Decoding runs entirely in your browser. The token is split, the header and payload are Base64URL-decoded, and the parsed JSON is shown in the tab. Treat the JWT as you would any secret: rotate tokens that you suspect have been exposed.

Are the generated passwords actually random?

Yes. The password generator uses the Web Crypto API's getRandomValues function, which is the same cryptographically secure source browsers use for TLS key material.

Why does the regex tester sometimes flag a pattern as invalid?

The tester runs your regex against the JavaScript engine. Patterns that work in PCRE, Python, or Go can use syntax JavaScript does not support, such as recursive groups or possessive quantifiers.

How does the cron explainer handle non-standard fields?

It supports the five-field POSIX form plus optional seconds and year fields used by Quartz and similar schedulers. Step values, ranges, lists, and weekday names all parse correctly.

Does the SQL formatter run my query?

No. It only formats the SQL text. There is no database connection of any kind. Parsing is done by a JavaScript SQL formatter that understands MySQL, PostgreSQL, T-SQL, and standard ANSI dialects.

Can the CIDR calculator handle IPv6?

It focuses on IPv4 ranges, which covers the bulk of subnet planning work. IPv6 prefix planning uses a different mental model, and a dedicated calculator usually serves it better.

Are slugs reversible?

No. Slug generation lowercases, removes diacritics, collapses whitespace, and strips characters that browsers escape in URLs. The original capitalization and punctuation cannot be recovered from the slug.

Complete guide to developer tools

What are developer tools?

Developer tools are small utilities that help with the daily grind of writing and shipping software: decoding tokens, testing patterns, parsing schedules, formatting data, planning networks, calculating permissions, and generating credentials. Each one runs in your browser so you can stay inside the workflow without context-switching to a separate app.

When to use them

These utilities cover the moments when looking up syntax or running a one-off calculation would otherwise interrupt real work.

Inspecting a JWT during an authentication bug investigation.
Tuning a regex against sample input before committing it to a parser.
Reading a cron string from a CI pipeline and seeing the next five run times.
Calculating a /24 subnet split for a new VPC.
Translating chmod 755 into rwxr-xr-x or vice versa.
Generating a memorable but strong password for a service account.
Formatting a SQL query pasted from a slow-query log.

Browser-based versus server-based

Developer utilities usually take small inputs and produce small outputs. Network round trips to a remote service add visible latency that often exceeds the cost of the computation itself. Running locally inside the tab removes that wait.

Privacy matters for a subset of these tools. JWTs frequently contain user identifiers and claim sets that should not be pasted into a third-party site. Generated passwords are by definition secrets that should reach as few systems as possible. Browser-based generation keeps the secret on the device that will eventually use it.

Server-side approaches still hold value for tasks that need a real environment: querying a database, hitting a live API, or running a large compilation. The tools here cover the parts of the job where a small library and your browser are enough.

Tool comparison

Tool	Primary use	Output / options
JWT decoder	Decode token header and payload	JSON output, expiry shown
Number base converter	Convert between bases	Binary, octal, decimal, hex
Regex tester	Test patterns	Match, replace, split modes
Cron explainer	Parse schedule into English	Next run times
HTML entity encoder	Encode special characters	Named or numeric entities
Markdown previewer	Render Markdown to HTML	Live preview
SQL formatter	Beautify queries	MySQL, PostgreSQL, T-SQL, ANSI
CIDR calculator	Subnet planning	Network, broadcast, host range
Chmod calculator	Unix permission bits	Numeric and symbolic
Password generator	Generate credentials	Random, strong, memorable
YAML formatter	Format and validate YAML	Kubernetes, CI, OpenAPI
XML formatter	Pretty-print XML	DOMParser-based
Slug generator	URL-safe slugs	Diacritic handling

Common workflows

Debug a failing auth request. Capture the bearer token from a network panel, paste it into JWT decoder, then check the expiry timestamp against unix timestamp.

Set up a new scheduled job. Draft the cron in cron explainer, verify the next run times, then format the surrounding config with YAML formatter before committing.

Plan a small VPC. Calculate the subnet split with CIDR calculator, generate a unique stack identifier with UUID generator, and seed the bastion host login with password generator.

Specification primer

A handful of standards underpin these tools. JWTs follow RFC 7519: three Base64URL-encoded parts separated by dots, signed with the algorithm declared in the header. Cron syntax is informally standardized through Vixie cron and POSIX, with extensions in Quartz and Jenkins.

CIDR notation comes from RFC 4632 and replaces the older classful network model. Unix permissions use a nine-bit mask split into owner, group, and other; the chmod calculator simply shows both numeric and symbolic forms in parallel.

SQL has multiple competing dialects but ANSI SQL covers the common subset. The formatter here understands dialect-specific keywords (MySQL backticks, PostgreSQL dollar quoting, T-SQL square brackets) without rejecting input that mixes them.

Frequently asked questions

What counts as a developer tool?: Any small utility that helps debug, format, validate, or generate code-adjacent content. The category covers token decoders, expression testers, schedule parsers, format validators, network calculators, permission helpers, and credential generators.
Is it safe to paste a real JWT into the decoder?: Decoding runs entirely in your browser. The token is split, the header and payload are Base64URL-decoded, and the parsed JSON is shown in the tab. Treat the JWT as you would any secret: rotate tokens that you suspect have been exposed.
Are the generated passwords actually random?: Yes. The password generator uses the Web Crypto API's getRandomValues function, which is the same cryptographically secure source browsers use for TLS key material.
Why does the regex tester sometimes flag a pattern as invalid?: The tester runs your regex against the JavaScript engine. Patterns that work in PCRE, Python, or Go can use syntax JavaScript does not support, such as recursive groups or possessive quantifiers.
How does the cron explainer handle non-standard fields?: It supports the five-field POSIX form plus optional seconds and year fields used by Quartz and similar schedulers. Step values, ranges, lists, and weekday names all parse correctly.
Does the SQL formatter run my query?: No. It only formats the SQL text. There is no database connection of any kind. Parsing is done by a JavaScript SQL formatter that understands MySQL, PostgreSQL, T-SQL, and standard ANSI dialects.
Can the CIDR calculator handle IPv6?: It focuses on IPv4 ranges, which covers the bulk of subnet planning work. IPv6 prefix planning uses a different mental model, and a dedicated calculator usually serves it better.
Are slugs reversible?: No. Slug generation lowercases, removes diacritics, collapses whitespace, and strips characters that browsers escape in URLs. The original capitalization and punctuation cannot be recovered from the slug.

Related concepts

Web Crypto API powers password and UUID generation.
Base64 encoding underpins JWT structure.
Regular expression covers regex theory and engines.
Data tools guide pairs with JSON and hashing workflows.
Text tools guide shares regex patterns and case handling.

Reviewed and tested May 25, 2026.