Free online developer tools can help with API requests, JSON inspection, regex checks, formatting, data conversion, text comparison, diagrams, and performance or network checks. This guide groups useful examples by task rather than claiming a verified inventory of 100 tools: the available sources describe 43 tools in one collection and a changing set of Postman utilities, but do not establish 100 distinct services with current free access.
“Free” can mean a one-off browser utility, a service with usage limits, or a free account that unlocks saved workflows. Likewise, browser-based does not automatically mean private: check where a particular tool processes data before entering credentials, customer information, or production payloads.
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Choose a tool by the job you need to do
A formatter, a regex tester, and an API client are not interchangeable. Use the tool category that matches the immediate task, then check the provider’s current supported formats, protocols, account requirements, and data handling.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minute- Inspect or transform structured data: start with a JSON or YAML formatter, validator, tree viewer, or query playground.
- Try a pattern or improve code style: choose a regex tester, language formatter, or linter.
- Send requests or examine integrations: use an API client or webhook inspector.
- Produce or compare artifacts: use generators, text diff tools, or diagram editors.
- Check a live site or service: use performance, uptime, SSL, DNS, or HTTP-header utilities.
Design, test, and troubleshoot APIs
Postman browser tools
Postman’s online tools cover API design and testing tasks. Its page lists an API Designer for OpenAPI 3.1, an OpenAPI editor/visualizer and validator, cURL-to-code and JSON-to-types converters, mock APIs, clients for REST, SOAP, SSE and other HTTP APIs, plus GraphQL, WebSocket, Socket.IO, gRPC, and MCP clients. It also lists health, uptime, speed, SSL certificate and HTTP header checks, load-test and requests-per-second tools, test-data generation, webhook utilities, and secret redaction.
#1 Best Overall
Postman says every tool on that page works without an account or installation. That statement applies to the listed tools, not every part of the Postman platform: its fuller workflows, including Spec Hub, monitors, performance testing, and Collection Runner, are associated with a free account. Postman also says some tools run locally while others use Postman services, so check the individual tool before submitting sensitive data.
Other API and webhook examples
A GitHub developer-tools directory names Hoppscotch as an open-source browser API ecosystem, ReqBin for sending requests, httpbin for client experiments, Webhook.site for inspecting inbound webhooks, and curlconverter for translating cURL commands. These are directory descriptions, not guarantees of current features or free-tier terms; consult each service directly before relying on a particular capability.
Format, validate, and explore JSON or YAML
For quick readability and syntax checks, DevToolHub lists JSON formatting and beautifying, validation, and tree viewing, as well as JSON-to-YAML, JSON-to-CSV, and YAML-to-JSON conversion. The project describes its collection as 43 free browser-based developer tools; that is the project’s own count, not an audited count of the broader tool market. It says its tools run client-side, but verify the behavior of the specific utility you use.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallOther examples in the developer-tools directory include JSONLint for formatting and validation, JSON Crack for graph-style exploration, JSON Path Finder, and jq play. A formatter is suited to cleaning up a document or locating syntax errors; a graph or tree view helps navigate nesting; a query playground helps extract values. Those are different jobs, even when the input is the same JSON file.
Test regular expressions, format code, and lint
Regex testers
DevToolHub lists a regex tester, while the directory includes regex101, Regexr, and Debuggex. Use a tester to try a pattern against sample text and inspect how it matches. Regex flavors and explanatory features vary, so confirm that the service supports the language or engine your application uses before treating a result as definitive.
Formatters and linters
The directory names the official Prettier Playground, Black Playground, ShellCheck, SQL Formatter, and HTMLHint. Formatters reshape source according to formatting rules; linters flag possible issues. Check the specific service for language/version coverage and options before applying its output to a project.
Encode, convert, and generate useful values
DevToolHub and the directory list utilities for Base64, URL, and HTML entity encoding or decoding, along with CyberChef for a broad range of data operations. They also name UUID generators, cron expression tools, Unix timestamp converters, and placeholder-data generators. A separate directory list includes README, gitignore, and code-image generators.
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These utilities address different transformations: encoding or decoding changes a representation, a timestamp converter changes how a time value is displayed, and a generator creates a new value or artifact. Verify input limits and output format on the selected service, especially when generated values feed production systems.
Compare text and draw diagrams
Text comparison
The directory lists online text comparison tools and Meld, a desktop option. A browser diff is convenient for a quick comparison; if the text is sensitive, use a tool whose data-handling behavior you understand rather than assuming pasted content remains on your device.
Diagrams and visual models
Browser diagram examples in the directory include Excalidraw, diagrams.net, Mermaid Live Editor, D2 Playground, and dbdiagram.io. They cover different ways of expressing visual or structured diagrams; check each provider for current export formats, account requirements, and whether edits are processed locally or remotely.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check page performance and network behavior
For page-performance work, the directory names PageSpeed Insights, GTmetrix, WebPageTest, and Chrome Lighthouse. They are examples of performance-checking options, not a measured ranking. Results can depend on the test setup and the service’s current behavior, so use the report’s stated conditions when comparing runs.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →For API and network checks, Postman’s tools page lists uptime and speed checks, SSL certificate checks, HTTP header checks, health checks, and load-test/RPS utilities. The directory also points to DNS and network tools. Confirm present limits, supported targets, and account requirements with the provider before using a check as an operational monitor or load test.
Best Value
Check privacy and access before pasting data
“Online” describes how you reach a utility, not necessarily where it runs. DevToolHub says its tools execute client-side; Postman says some of its tools run locally and others use Postman services. Those statements apply to those providers’ stated tools and do not establish the behavior of other services in this guide.
- Do not paste production tokens, passwords, private keys, customer records, or confidential payloads into an unfamiliar utility.
- Look for the provider’s data-processing or privacy information for the exact tool, not just a general claim about its product suite.
- Check whether a tool is genuinely usable without an account, whether a free account is needed for saved or recurring work, and whether limits apply.
- For project-critical work, verify current protocol, language, format, region, and export support on the provider’s own page.
Can this be a verified “100+” tool list?
Not on the evidence available here. DevToolHub describes 43 tools, while the GitHub directory is a curated category list rather than a verified inventory of 100 distinct services. Postman’s page is dynamic: a search result described 32 tools at one point, while the opened page showed an expanded list. Those figures are not a reliable combined count of unique, currently free tools.
The practical takeaway is to browse by task and confirm each service’s current terms. A count of 100 would require checking that every entry is distinct and that its present access model and availability qualify as free.
Recommended Free Tools
Quick Recap
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