HDL BlockSeal
HDL BlockSeal is a VS Code extension that automatically inserts the matching closing keyword whenever you press Enter at the end of an opening block line in a hardware description language file. It works for Verilog, SystemVerilog, and VHDL, respects your indentation settings, and is smart enough not to insert a duplicate if the closing keyword is already present.
How it works
When you press Enter at the end of an opening block line, the extension:
- Inserts a blank indented line and places your cursor there — ready to type
- Inserts the matching closing keyword on the line below, at the correct indentation level
- Does nothing if a matching closing keyword already exists in scope (no duplicates)
// Before (cursor at end of line, press Enter):
module counter(input clk, output reg q);
// After:
module counter(input clk, output reg q);
│ ← cursor, ready to type
endmodule
// Before:
always @(posedge clk) begin
// After:
always @(posedge clk) begin
│ ← cursor
end
// Before (indented block):
if (rst) begin
// After:
if (rst) begin
│ ← cursor, indented one level deeper
end
Supported languages and triggers
Verilog and SystemVerilog
| Opening line (press Enter after) |
Closing keyword inserted |
module NAME ... |
endmodule — at column 0 |
interface NAME ... |
endinterface — at column 0 |
class NAME ... |
endclass — at column 0 |
package NAME ... |
endpackage — at column 0 |
program NAME ... |
endprogram — at column 0 |
primitive NAME ... |
endprimitive — at column 0 |
config NAME ... |
endconfig — at column 0 |
Any line ending in begin |
end — same indent as opener |
fork |
join — same indent as opener |
function ... |
endfunction — same indent as opener |
task ... |
endtask — same indent as opener |
checker NAME ... |
endchecker — same indent as opener |
clocking NAME ... |
endclocking — same indent as opener |
covergroup NAME ... |
endgroup — same indent as opener |
property NAME ... |
endproperty — same indent as opener |
sequence NAME ... |
endsequence — same indent as opener |
generate |
endgenerate — same indent as opener |
specify |
endspecify — same indent as opener |
table |
endtable — same indent as opener |
The begin trigger covers every common usage pattern:
always @(posedge clk) begin
initial begin
if (condition) begin
else begin
else if (condition) begin
for (i = 0; i < N; i++) begin
while (condition) begin
forever begin
begin : block_label
VHDL
| Opening line (press Enter after) |
Closing keyword inserted |
entity NAME is |
end entity NAME; — at column 0 |
architecture NAME of ENTITY is |
end architecture NAME; — at column 0 |
package NAME is |
end package NAME; — at column 0 |
package body NAME is |
end package body NAME; — at column 0 |
configuration NAME of ENTITY is |
end configuration NAME; — at column 0 |
[LABEL :] process (...) |
end process; — same indent as opener |
[LABEL :] ... generate |
end generate; — same indent as opener |
function NAME ... |
end function NAME; — same indent as opener |
impure function NAME ... |
end function NAME; — same indent as opener |
procedure NAME ... |
end procedure NAME; — same indent as opener |
component NAME |
end component NAME; — same indent as opener |
[LABEL :] block |
end block; — same indent as opener |
VHDL keyword matching is case-insensitive (ENTITY, entity, and Entity all trigger correctly).
Indentation behaviour
- Top-level constructs (
endmodule, endinterface, endclass, endpackage, endprogram, endprimitive, end entity, end architecture, etc.) are always placed at column 0, regardless of how the opening line is indented.
- Block constructs (
end, endfunction, endtask, end process, etc.) are placed at the same indentation level as the opening line.
- The cursor lands on the blank line between the opener and the closing keyword, indented one level deeper than the opener — ready to type.
- Indentation style (spaces or tabs) and tab size are read directly from your VS Code editor settings. No configuration needed.
Duplicate detection
The extension tracks whether a matching closing keyword already exists in scope before inserting anything.
- For top-level constructs, it scans the rest of the document for the closing keyword.
- For indented blocks, it scans downward until it exits the current indentation scope.
This means pressing Enter on a line inside an already-complete block (or anywhere above an existing closing keyword) does nothing — no duplicates are ever inserted.
Requirements
- VS Code 1.60 or later
- No internet connection required — fully local, zero runtime dependencies
Installation
From the VS Code Marketplace
Search for HDL BlockSeal in the Extensions panel (Ctrl+Shift+X) and click Install.
From a .vsix file
- Download the latest
.vsix from Releases
- Open the Command Palette (
Ctrl+Shift+P) → Extensions: Install from VSIX… → select the file
Build from source
git clone https://github.com/VENOMNBB/HDL-BlockSeal.git
cd HDL-BlockSeal
npm install -g @vscode/vsce
vsce package
code --install-extension hdl-blockseal-1.0.0.vsix
Settings
All settings are under the hdlBlockSeal namespace and take effect immediately without reloading VS Code.
| Setting |
Type |
Default |
Description |
hdlBlockSeal.enable |
boolean |
true |
Master switch — disabling this turns off the extension for all languages |
hdlBlockSeal.enableVerilog |
boolean |
true |
Enable for Verilog (.v) files |
hdlBlockSeal.enableSystemVerilog |
boolean |
true |
Enable for SystemVerilog (.sv, .svh) files |
hdlBlockSeal.enableVHDL |
boolean |
true |
Enable for VHDL (.vhd, .vhdl) files |
To change a setting, open File → Preferences → Settings and search for hdlBlockSeal, or add the following to your settings.json:
{
"hdlBlockSeal.enable": true,
"hdlBlockSeal.enableVerilog": true,
"hdlBlockSeal.enableSystemVerilog": true,
"hdlBlockSeal.enableVHDL": true
}
Known limitations
- The extension reacts to a single newline insertion at a time. Pasting multi-line text does not trigger block closing.
- Comments containing block keywords (e.g.
// module foo) are not parsed and do not trigger the extension.
- The extension does not attempt to match opening and closing keywords across files.
License
MIT — see LICENSE for details.
