Small Tools

Small Tools is a set of free developer utilities for the small, repetitive tasks in everyday engineering work. You paste data, run a tool, and read the result: formatting and validating data, decoding tokens and encoded values, comparing API contracts, converting timestamps, testing patterns. It is a separate site with its own privacy, cookie, and terms pages. For that product, those pages take precedence over the policies on this site.

What you can do with it

The tools are grouped here by task. These are examples, not the full list; the Small Tools site lists everything that is currently available. Each tool page explains what it accepts and what it does not do.

Check and format data

• JSON Formatter: format JSON with readable indentation.
• JSON Validator: check JSON syntax and read the parsing error.
• JSON Diff: compare two JSON documents.

These check syntax and structure. They do not tell you whether the data is correct for your application. Our note on JSON validation pitfalls shows where parsers disagree.

Inspect a token or an encoded value

• JWT Decoder: decode a token's header and payload. It does not verify the signature.
• JWT Expiration Checker: read the exp claim and compare it with your device's clock.
• Base64 Decoder and URL Decoder: decode Base64 text and percent-encoded URL components.

Decoding shows what a token claims, not that it is genuine. See JWT verification mistakes for what a real verifier must check.

Review an API contract

• OpenAPI Validator: check that an OpenAPI document is valid YAML or JSON with the essential structure.
• OpenAPI Diff: compare endpoint and operation changes between two documents.
• OpenAPI Breaking Change Checker: flag removed operations and newly required request fields.

These cover selected changes only. Response-side changes need a deliberate review; see Judging OpenAPI breaking changes.

Time and patterns

• Unix Timestamp Converter: convert Unix timestamps in seconds or milliseconds to readable dates.
• Regex Tester: test a regular expression against sample text and inspect the matches.

Network information

• What Is My IP and DNS Lookup: look up your connection's address and public DNS records.

These two cannot work entirely in the browser. See the next section.

Example: a failing API request

A workflow that uses several of the tools together. The tools help you look; they do not connect to your API and they do not replace tests.

1. Paste the request body into the JSON Validator and fix the syntax error it reports.
2. Decode the bearer token with the JWT Decoder and compare iss, aud, and exp with what the API expects. Remember that the decoder does not check the signature.
3. If the failure started after an API release, compare the old and new contracts with the OpenAPI Diff and the Breaking Change Checker.
4. Confirm the fix with your own application's tests.

How your input is handled

• Formatting, conversion, and calculation tools process your input in your browser. According to the Small Tools privacy policy, that input is not uploaded to its application servers and is not included in analytics.
• What Is My IP and DNS Lookup send a request to an endpoint hosted on Cloudflare, because they need information a browser cannot compute locally. The policy says DNS Lookup sends the domain or record name you enter, and only when you start a lookup.
• Page loads and analytics. Loading a page makes ordinary requests for the site's files, and Small Tools uses Cloudflare Web Analytics to understand aggregate usage. Its policy describes both.
• You can check this yourself. On October 20, 2026 we watched the network requests of the JSON Formatter page and saw no request when it formatted sample input. That is evidence for one page, one input, and one moment, not a guarantee. Our note explains how to run the same test and what it does and does not prove.

Even when a tool runs locally, use redacted or test values for real tokens, keys, and customer data. If this summary and the product's own privacy policy differ, the product's policy applies.

Free, and how it is supported

Small Tools is free to use and needs no account. Some of our free products may display ads served by third parties such as Google. Advertising helps keep them free, but ads are not endorsements and advertisers have no influence over how the tools work or how we describe them. See the Privacy Policy and Cookie Policy.

Learn alongside the tools

• Our engineering notes cover problems the tools touch, with examples we ran.
• The Small Tools site has its own developer guides and an updates page.

Feedback

Found a wrong result or have an idea for a tool? Tell us. Please include the tool's URL and a minimal, redacted example, never live credentials.