Hex Editor Tool

The Hex Editor is a built-in tool in HL7Spy that lets you view and edit the raw bytes of a file or HL7 message in a side-by-side hexadecimal / ASCII layout. It is most commonly used to:

• Inspect the exact bytes that make up a message, including non-printable characters, line endings (CR, LF, CRLF), and encoding markers such as BOMs.

• Diagnose framing issues (MLLP start/end blocks, segment separators, embedded nulls, etc.).

• Locate and jump to a specific byte offset in a large file.

• Make small targeted byte-level corrections to a file and save them.

Tip

The Hex Editor is intentionally a low-level tool. If you just want to read or edit the content of an HL7 message, use the standard Message Editor. Use the Hex Editor when you need to see or change the underlying bytes.

Open

Opening the Hex Editor

There are several ways to open the Hex Editor, depending on what you want to inspect.

1. Open an arbitrary file in the Hex Editor

1. On the ribbon, click Open Hex in the File Operations group.

2. Pick a file from the Open File dialog.

The default filter shows *.hl7, *.txt and *.log files, but you can switch to All files (\.\) to open any file on disk.

You can also:

• Press the Ctrl keytip for the Open Hex button (H) when the ribbon is active.

• Click the drop-down arrow next to Open Hex to pick a recently opened hex file from the Recent Hex Files list.

• Drag and drop a single file onto the Hex Editor window.

2. Inspect the current HL7 message as hex (read-only)

From an open message in the Message Editor:

1. Select the field, segment, or range of text you want to inspect (optional).

2. Open Message Properties (which launches the Hex Editor view of the current message).

The Hex Editor opens in read-only mode with the underlying message bytes loaded. If the message still maps to a file on disk and has not been modified, the editor opens the file directly and highlights the current selection (field or manually selected range). If the message has been modified in memory, the editor shows a snapshot of the in-memory bytes and the status bar displays:

Message has been modified by the user

3. Hex Editor from the Open Folder view

From the Open Folder tool:

1. Right-click on any file in the file list.

2. Choose the option to open the file in the Hex Editor.

The Hex Editor window

The window is divided into three regions:

Hex view layout

• Line offsets (left column) show the byte offset of the first byte on each line.

• Hex bytes (middle column) show the bytes in hexadecimal. You can edit bytes in place by clicking a byte and typing two hex digits.

• String view (right column) shows the ASCII interpretation of the same bytes. Non-printable bytes are shown as a placeholder character. You can also type directly into the string view to replace bytes.

• Group separators and a column header (column numbers 0-F, 0-17, etc.) are shown above the hex area to make alignment easier.

Tip

Click anywhere in the hex area or the string view to move the caret. The other column automatically scrolls to the matching position.

Toolbar reference

The toolbar at the top of the Hex Editor exposes the most common actions.

Note - Read-only files and messages

When a file is opened read-only (because the file is locked, marked read-only on disk, or because the Hex Editor was launched from Message Properties), the Save, Revert, Cut and Paste buttons remain disabled. You can still search, navigate, and copy bytes.

Status bar reference

The status bar at the bottom of the window shows live information about the file and caret.

Finding bytes or text

Click Find or press Ctrl+F to open the Find dialog.

The dialog has two search modes that are selected automatically based on which field you are typing in:

• Text - type a string in the Text box. By default the search is case-insensitive. Tick Match Case to make it case-sensitive.

• Hex - type a sequence of hex bytes in the Hex box (for example 0D 0A 0B or 0d0a0b). The search is byte-exact.

Clicking OK starts the search from the current caret position and selects the next match. If no match is found, the message End of File Reached is shown.

Finding subsequent matches

• After the first match, press F3 (or click Find Next) to find the next occurrence without re-opening the dialog.

• Find Next reuses the last entered search, so you can keep stepping through all hits.

Cancelling a long search

Searching a very large file can take several seconds. While the search is running:

• A progress bar appears on the right side of the status bar.

• Press Escape to abort the search.

• Inside the Find dialog, click Cancel while the search is running to abort it.

Jumping to a specific offset

Click Go To or press Ctrl+G to open the Go To dialog. Enter a byte number and click OK (or press Enter).

The value is 1-based: entering 1 jumps to the first byte of the file. The maximum accepted value is the file size. The default value shown in the dialog is the current caret position, so you can quickly adjust to a nearby offset.

Editing bytes

When the file is writable:

1. Click the byte you want to change (in either the hex or the string column).

2. Type the replacement value:

   • In the hex column, type two hex digits.

   • In the string column, type a printable character.

3. Use Cut, Copy, and Paste for larger edits.

The title bar and the Save button reflect pending changes. Use Save to commit changes to disk, or Revert / Ctrl+Z to discard all changes and reload the file.

Closing with unsaved changes

If you close the Hex Editor while there are unsaved changes, HL7 Spy prompts:

• Yes - Save changes and close.

• No - Discard changes and close.

• Cancel - Return to the editor with changes intact.

Keyboard shortcuts

Standard text-editing shortcuts also work in the hex view:

Appearance and layout

• Bytes per line can be set to Auto (default), 16, 24, or 32 via the toolbar. Auto adjusts as you resize the window.

• The Hex Editor respects the currently selected HL7 Spy theme. When you change the application theme, the editor colors update automatically.

• The monospace font used by the hex view is fixed at runtime to keep columns aligned.

Tips and gotchas

Tip - Use Hex Editor to spot hidden characters

Segment terminators in HL7 are carriage returns (0x0D). The Hex Editor makes it obvious when a file uses CRLF (0x0D 0x0A) instead of CR only, or when stray whitespace / BOM bytes have been added by another tool.

Warning - Large files

For very large files, switching to 16 Byte or 24 Byte mode can make the file easier to scan visually, and keeps the line count predictable. Searches on multi-gigabyte files can take a while - watch the progress bar and remember that Escape cancels the search.

Note - Read-only when launched from a message

When the Hex Editor is launched from Message Properties, it is always read-only, even when the underlying file is writable. This is by design, to prevent accidental edits while inspecting a message. To edit the underlying file, close that window and reopen it using Open Hex from the ribbon.