Here is my list of free Windows tools for SharePoint Online development that can make a developer or consultant more productive.
This post contains well known tools to the SharePoint community so it is more for a beginner SharePoint developers. I will try to keep this list updated.
SharePoint Online tools and extensions for more productivity
SharePoint Search Query Tool - https://github.com/SharePoint/PnP-Tools/tree/master/Solutions/SharePoint.Search.QueryTool
This tool is a must for SharePoint Search driven development scenarios. A search query can quickly be tested and even copied and adjusted in a SPFx webpart for example. It is also useful for Search Keyword Query Language (KQL) learning and how to call the search api with different parameters. I didn't even know half of the parameters you can include in query before started using the tool. Recently, support for Microsoft Office Graph has been added. I use it daily and it works with SharePoint on-premises installations as well.
CAML Designer - https://www.biwug.be/resources
Very useful for building CAML queries and calling SharePoint CSOM REST services. SharePoint lists and document libraries can be explored quickly and the designer displays the executed script so it can be copied either as CAML (XML) or as SharePoint OData REST query (CSharp and PowerShell snippets also available) in your custom solution.
SharePoint Client Browser for SharePoint Online and SharePoint Server - https://spcb.codeplex.com
Should you know what is going on in a Site Collection or Tenant? Download this tool and browse through the SharePoint objects. From site properties to list event receivers this tool shows everything you need to know about site components. A good feature is that you can explore the tenant properties if you have tenant admin access. It can get the XML schema of some of the SharePoint components. The XML schemas can be useful when we have to provision assets (content types, site columns, lists, libraries or other elements) for SPFx web part.
SP Editor Tool (Chrome extension) - https://chrome.google.com/webstore/detail/sp-editor/ecblfcmjnbbgaojblcpmjoamegpbodhd
A multipurpose tool that can execute pnp js REST calls directly within the chrome browser with Intellisense support even in production. It is one VERY POWERFULL tool and should be used carefully, but again it is perfect for running pnp js scripts, site quick checks, adding web properties, quick add of webhook and more directly into the browser.
Demo on how to use it
It is available on Github
really good one for managing Property Bags, Search ReIndex, Hidden Lists, and so on: https://chrome.google.com/webstore/detail/chrome-sp-dev-tools/efhiadiopfkjpdihdmlccoffnpdblkho?hl=en-GB
Chrome developer tools
Visual Studio extension for SharePoint Framework projects - https://github.com/SharePoint/sp-dev-fx-vs-extension
The transition from old school full trust SharePoint solutions developer to the new upgraded Nodejs-Typescrypt-Yeoman-React-Gulp-Webpack developer may not be easy.
Some of us (ex Web Forms developers) are way too used with the Visual Studio IDE and we still prefer the VS tools rather than the new trend of being a Command Line-Keyboard ninja. Thanks to @paulschaeflein and @eshupps we have Visual Studio extension for SharePoint Framework projects in preview that allows to scaffold and run SPFx webparts in Visual Studio.
Host application for Windows PowerShell. Very good tool for PowerShell beginners and even advanced devops, since it is Windows built-in and has debugging support and tab completion.
Microsoft Azure Storage Explorer - http://storageexplorer.com
I use it to quickly upload or download Blob assets for my SPFx webparts CDN. This can be automated from the SPFx solution, but the tool is still handy for Azure Storage Account exploring.
HTTP/S Clients for CRUD calls
Postman - https://www.getpostman.com
Debugging HTTP/s proxy tool. I use it to analyze SharePoint REST APIs CRUD requests and responses. A good feature is that, I am able to save my CRUD queries and re-call them later.
Request Bin - https://requestb.in
RequestBin gives you a URL that will collect requests made to it and let you inspect them in a human-friendly way.
Use RequestBin to see what your HTTP client is sending or to inspect and debug webhook requests.
Microsoft Graph Explorer - https://developer.microsoft.com/en-us/graph/graph-explorer
Microsoft Graph Explorer can be used for testing Microsoft Graph APIs endpoints. It is handy because I do not need to do OAuth2, get access token and then send authenticated request, but I can login to the explorer and quickly test a Graph endpoint.
Still in use in some scenarios
SharePoint Designer - https://www.microsoft.com/en-us/download/details.aspx?id=35491
I would say that the designer can still be useful for a quick fix on classic SharePoint page or SharePoint 2013/2010 workflow quick edit. Please note that it will not be supported with modern SharePoint sites based on Office 365 Groups. More information on this link.
SharePoint Color Palette Tool - https://www.microsoft.com/en-us/download/details.aspx?id=38182
Provides color palette functionality for use with SharePoint composed looks.
Handy Tools or plugins
Cmder - http://cmder.net
Cmder is a software package created out of pure frustration over the absence of nice console emulators on Windows. I mainly use it for full console screen on older versions of Windows :).
Open Command Line - https://marketplace.visualstudio.com/items?itemName=MadsKristensen.OpenCommandLine
Opens a command line in Visual Studio at the root of the project with a very handy keyboard shortcut ALT+SPACE. Support for all consoles such as CMD, PowerShell, Bash etc. Provides syntax highlighting, Intellisense and execution of .cmd and .bat files. Support for Cmder as well.
More tools ... frameworks
I will not mention universal tools like Visual Studio Code or Visual Studio 2017 because I think they are must for every ASP.NET developer.
The list does not include any libraries or frameworks. I can do it in another post later, but if you haven't heard about SharePoint Patterns and Practices, please visit this - https://github.com/SharePoint/PnP. It is a pack of SharePoint Frameworks and Tools that are must for a modern SharePoint developer.
A SharePoint developer or consultant can be very productive with the right skill set and the right tools. Have a try, if some of the mentioned above can make you more productive in your daily challenges.
Please add more useful tools in the comments below if you think they deserve to be in the list.