Packet Sender Documentation

Packet Sender is an open source utility to allow sending and receiving TCP and UDP packets. Packet Sender can also send SSL (encrypted TCP) packets. The mainline branch officially supports Windows, Mac, and Desktop Linux (with Qt). Other places may recompile and redistribute Packet Sender. Packet Sender is free and licensed GPL v2 or later. It can be used for both commercial and personal use.


  • Controlling network-based devices in ways beyond their original apps
  • Test automation (using its command line tool and/or hotkeys)
  • Testing network APIs (using the built-in TCP and UDP clients)
  • Malware analysis (using the built-in UDP and TCP servers)
  • Troubleshooting secure connections (using the SSL client).
  • Testing network connectivity/firewalls (by having 2 Packet Senders talk to each other)
  • Tech support (by sending customers a portable Packet Sender with pre-defined settings and packets)

Some knowledge of basic network protocols is a prerequisite to using Packet Sender. Beyond that, Packet Sender was designed to be very easy to use. Simply start using it.


Portable Mode

Packet Sender has a "portable" mode. At launch, it will look for packets.ini and ps_settings.ini in its run-time directory. Windows users, this directory is the same place as the .exe. For Mac users, this run-time directory is at "". If INI files are found, it will use them instead of %APPDATA%" or "Library/Application Support".

IPv4 and IPv6 Support

By default, Packet Sender's built-in servers are configured to support IPv4. If you wish to use IPv6, there is a toggle switch at the bottom right. Click to switch between IPv4 / IPv6.

Packet Sender IP Mode Toggle

Packet Sender's GUI client sender and CLI will detect the type of IP address being used and bind appropriately to send the packet. Note that you must include a scope ID to send.

Documentation (GUI)

Packet Sender is identical for all the desktop versions. The only difference is its theme to match the operating system.

Packet Sender screenshot

  • In the bottom right, there are UDP server and TCP server status and port. You can click to activate or deactivate these. There is no built-in SSL server.
  • There is also IPv4 Mode and IPv6 Mode. Click to toggle between server modes.
  • During packet resending, there will be a button to cancel all resends.
  • Please check your firewall. Windows aggressively blocks TCP-based servers. Packet Sender will still work if the firewall blocks it, but it can't receive unsolicited TCP-based packets.
  • In the table, there is a list of saved packets. You can double-click to directly edit fields in this table.
  • Select multiple packets to enable "Multi-Send". Selected packets are shown in a quick-send area above the traffic log.
  • Fields can be rearranged by drag-and-drop in the settings menu.
  • A resend value of "0" means it is a single-shot packet.
  • A packet has a name, destination address (domain names are default resolved just before sending), port, and data associated with it.
  • Click "Send" to immediately send. Click "Save" to send later.
  • For IPv6 sending, you will also need the scope ID.
  • Packet Sender supports mixed ASCII and HEX notation:
    • \XX gets translated to XX in hex
    • \n, \r, \t will get translated to 0A, 0D, and 09
    • HEX numbers are space delimited
    • The HEX field will attempt to interpret other common delimiters (such as commas, colons (Wireshark), semicolons, " 0x", etc) and auto-correct.
    • A single stream of HEX is also supported. If the number of bytes is odd, Packet Sender will assume the front byte needs a zero and then auto-correct.
    • Example ASCII: hello world\r
    • Example HEX: 68 65 6c 6c 6f 20 77 6f 72 6c 64 0d
    • You may save a packet directly from the traffic log. You will be prompted for a name, and the source address and port will be switched for your convenience.
    • You may also load a file directly in to the HEX field. The HEX field supports sending up to 10,922 bytes. The theoretical limit for sending via the command line is 200 MB.
  • An optional response can be sent. The same response is used for TCP and UDP.

Hotkeys / Keyboard Shortcuts

The fields at the top can be navigated using CTRL+1, CTRL+2, etc, up to CTRL+8 (send button). On Mac, the shortcut key is Command.

Some notes:

  • When you navigate to the TCP/UDP/SSL option, you may use up/down or t/u/s characters.
  • If you are going to automate with hotkeys (using tools such at AutoHotKey), you may want to turn off "Restore previous session".

SSL Client

Packet Sender supports establishing encrypted connections over SSL. This is supported in the GUI and on the command line. Some notes on this:

  • The certificate negotiation is handled immediately during connection.
  • By default, Packet Sender ignores all SSL errors (expired cert, wrong host name, self-signed, etc).
  • Packet Sender outputs the cert negotiation progress in to the traffic log.
  • Packet Sender outputs the encryption algorithm used in the traffic log (such as AES 128).

If available, on Windows, Packet Sender will use OpenSSL. On Mac, Packet Sender will use the native SSL libraries.

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (

Packet Sender Direct TCP

  • If there is an SSL error, Packet Sender will output it to the traffic log. If the setting is to continue anyway (default), it will continue to negotiate encryption. Otherwise, the connection ends with failure to connect.

Packet Sender Direct TCP

Smart Responses

Packet Sender supports up to 5 smart responses. To use it, disable normal responses. Packet Sender Direct TCP

  • Packet Sender will compare the packet within the encoding you choose.
  • Packet Sender translates the encoding before sending out the reply.
  • The available encodings are:
    • Mixed ASCII -- The standard Packet Sender way of encoding ASCII along with non-printable characters
    • HEX -- Packet Sender's normal HEX encoding
    • EBCDIC -- An encoding used mostly by IBM mainframes. The input field is normal Mixed ASCII and is translated when performing the comparison and sending.


Packet Sender supports these macros when sending responses:

  • {{DATE}} -- Sends the current date in "yyy-mm-dd" format.
  • {{TIME}} -- Sends the current time in "hh:mm:ss ap" format.
  • {{UNIXTIME}} -- Sends the current epoch time stamp.
  • {{RANDOM}} -- Sends a random number ranging from either 0 to 32767 or 2147483647, depending on 32-bit or 64-bit (default installer for Windows is 32-bit. Mac is 64-bit). Packet Sender will swap the macro with real values before sending.

Persistent TCP and SSL

Packet Sender supports persistent TCP and SSL connections via a separate UI dialog. It is enabled by checkbox on the main window or in the settings dialog.

Packet Sender Direct TCP and SSL

  • Any number of persistent connections can be created.
  • Previously saved packets can be loaded in the drop-down.
  • There is a "raw" view and "ASCII" view. The ASCII view is useful to troubleshoot data that is not printed by the raw view.
  • Traffic is also saved in the main window traffic log.
  • The timer in the bottom lefts starts as soon as a valid data packet is sent/received. It stops when the connection is closed.
  • You may optionally append a carriage return when you quick-send by hitting the return key. This is useful for command-prompt menus over TCP / SSL connections.
  • Incoming persistent connections to the server will launch the UI dialog.
  • During resend, the persistent connection packet is carried over to the new UI dialog. Clicking "Resending(1)" will cancel it.

Persistent connections are not supported via the command line.

IPv4 Subnet Calculator

Packet Sender has a built-in subnet calculator. It is under the Tools menu. Packet Sender Direct TCP

  • The log window will display non-loopback IPv4 and IPv6 addresses found on your computer.
  • The top left field allow inputting an IPv4 address.
  • The field below is for a subnet, either X.X.X.X or /XX notation.
  • The results of the calculation are on the right.
  • The field below is a quick check to see if an IPv4 is within one of your subnets.

Additional Configuration Options

  • IPv4 Mode or IPv6 Mode in the servers. This is identical to the toggle switch.
  • The traffic log and packet table is divided by a draggable splitter. This splitter can also be collapsed on either side.
  • Copy to the clipboard the raw packet data (default). If your data has a large amount of non-ASCII characters, you may prefer a translated version.
  • Resending can be auto-cancelled after X number of packets. Set to 0 to resend forever.
  • Traffic log can be set to roll at 100 entries.
  • Import/Export of packets is available via menus.
  • Attempt receive before send (some servers expect this behavior).
  • 500 ms delay before sending data (some servers are slow).
  • Enable keyboard shortcut for ASCII --> EBCDIC translation.
  • Resolve DNS during input. The default is to resolve DNS just before sending.
  • Ignore SSL errors. Packet Sender will note the error and continue with encryption. Otherwise, Packet Sender abandons the connection.

Documentation (Command Line)

The command line extension used in Windows installations is .com. Using .exe will launch the GUI. Leave off the extension and Windows will choose the correct program. The same executable controls the command line and GUI for Mac and Linux operating systems.

Packet Sender CLI screenshot

The command line system in Packet Sender follows the same pattern as other Linux utilities. It has a long name (such as --version) and a short name (such as -v). These options can be arranged in any order and Packet Sender will parse them correctly. The last 3 options are positional and must appear last. They are IP, port, and data. These last options are optional if using a stored packet.

packetsender --help
Usage: packetsender [options] address port data
Packet Sender is a Network TCP and UDP Test Utility by Dan Nagle
See for more information.

-?, -h, --help  Displays this help.
-v, --version   Displays version information.
-q, --quiet     Quiet mode. Only output received data.
-x, --hex   Parse data as hex (default).
-a, --ascii     Parse data as mixed-ascii (like the GUI).
-A, --ASCII     Parse data as pure ascii (no \xx translation).
-w, --wait <ms> Wait up to <milliseconds> for a response after sending. Zero means do not wait (Default).
-f, --file <path>   Send contents of specified path. Max 1024 for UDP, 10 MiB for TCP.
-b, --bind <port>   Bind port. Default is dynamic.
-t, --tcp   Send TCP (default).
-s, --ssl   Send SSL and ignore errors.
-S, --SSL   Send SSL and stop for errors.
-u, --udp   Send UDP.    
-n, --name <name>   Send previously saved packet named <name>. Other options overrides saved packet parameters.

-address    Destination address. Optional for saved packet.
-port   Destination port. Optional for saved packet.
-data   Data to send. Optional for saved packet.

Example CLI

packetsender -taw 500 22 "Hello\nWorld"
TCP (56620):// 48 65 6c 6c 6f 0a 57 6f 72 6c 64
Response Time:5:51:37.042 pm
Response HEX:53 53 48 2D 32 2E 30 2D 4F 70 65 6E 53 53 48 5F 35 2E 33 70 31 20 44 65 62 69 61 6E 2D 33 75 62 75 6E 74 75 33 2E 31 2E 49 53 2E 31 30 2E 30 34 0D 0A
Response ASCII:SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu3.1.IS.10.04\r\n

Example CLI using SSL and ignoring errors

The command line has the option to ignore or abandon on SSL errors. The default is to ignore.

packetsender -saw 500 443 "GET / HTTP/1.0\r\n\r\n"
SSL Error: The certificate has expired
SSL (54202):// 47 45 54 20 2f 20 48 54 54 50 2f 31 2e 30 0d 0a 0d 0a
Cipher: Encrypted with AES(128)

Response Time:3:24:55.695 pm
Response HEX:48 54 54 50 2f 31 2e 31 20 34 32 31 20 0d 0a 53 65 72 76 65 72 3a 20 6e 67 69 6e 78 2f 31 2e 31 30 2e 30 20 28 55 62 75 6e 74 75 29 0d
Response ASCII:HTTP/1.1 421 \r\nServer: nginx/1.10.0 (Ubuntu)\r


Missing a feature? You can hire me to add it to Packet Sender.


Packet Sender is currently accepting sponsors, either monetary or in-kind.


GPL v2 or Later. Contact me if you require a different license.


Packet Sender is wholly owned and copyright © - @NagleCode - -