CheckCon - Free HTTP & HTTPS Connection & Response Debugger

New in version 3.0

• HTTPS and TLS support - send the same hand-written request over a TLS connection, and see the negotiated protocol, cipher suite and the server's certificate details alongside the response. Self-signed and mismatched certificates can be accepted for testing internal servers.
• Request templates - start from a ready-made GET, HEAD, POST (form or JSON), PUT, PATCH, DELETE or OPTIONS request instead of typing one from scratch.
• Insert common headers - add Content-Type, Authorization, User-Agent, Cookie, Range, Referer and the rest from a menu, with Host and Content-Length filled in for you.
• Request checking - CheckCon warns you before sending if the header block does not end with a blank line, if Content-Length does not match the body, if the Host header is missing, or if a header line is malformed - and offers to correct it or to send it exactly as typed.
• Light, Gray and Dark themes, remembered between runs.
• Host, port, HTTPS and Send in every tab, so several endpoints can be worked on side by side.
• Recently used files in the File menu, plus word wrap and a line and column indicator.
• Rebuilt on .NET 8, with a faster, non-blocking send that returns as soon as the response is complete.

Features

Building requests

• Send raw HTTP and HTTPS requests to any host and port - you control every header and every byte
• Templates for the common request types, and one-click insertion of the common HTTP headers
• Content-Length kept in step with the request body automatically
• Optional validation before sending, with the option to send an invalid request deliberately

Reading responses

• View full raw responses exactly as returned by the server, headers and body
• Correct character set handling, so UTF-8 and other encodings are displayed properly
• TLS protocol, cipher suite and certificate subject, issuer, validity and thumbprint reported for HTTPS connections
• Content-Length and chunked responses recognised, so the response appears as soon as it is complete

Working with tests

• Multiple tabs for testing several connections simultaneously, each with its own host, port and HTTPS setting
• Save and reload tabs as XML for repeatable testing
• Recently used files listed in the File menu
• Right-click a tab to close it; unsaved tabs are flagged before they are closed
• Light, Gray and Dark themes, optional word wrap, and a line and column indicator
• Ideal for debugging connectivity, headers, and server behaviour
• Free to use

Why developers use CheckCon

It gives you complete visibility into what a server returns - without browser caching, hidden redirects, or tooling interference. Perfect for debugging APIs, testing endpoints, verifying TLS certificates, checking server availability, or diagnosing unexpected HTTP behaviour.

Because CheckCon sends exactly what you type, it is equally useful for the opposite job: deliberately sending a malformed or unusual request to see how a server handles it.

System requirements

• Windows 10 or later
• .NET 8 Desktop Runtime

Support

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