diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 7812d4846..6fd4450dc 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -23,6 +23,7 @@
 - Added `gJ` to join a line range, `gv` to restore the last visual selection, and `ZZ`/`ZQ` shortcuts for save-and-exit or exit-without-save in vim mode
 - Added paragraph text object `p` for `ip`/`ap`-style paragraph selection
 - Added support for Vim ex line-address forms like `.`, `$`, `+N`/`-N`, destination addresses such as `:t$`, and ranged `:global` commands
+- Added Vim ex `:join`/`:j` and `:join!`/`:j!` support to join addressed lines with or without whitespace normalization
 - Added a warning when chunk edits write to the `~` selector with body lines that appear over-indented, instructing users to start top-level body text at column 0
 - Added validation feedback for suspect indentation in chunk-mode `~` body writes so users can align content with the tool's automatic base indentation
 - Added support for multi-file `edit` calls across replace, patch, hashline, and chunk modes by grouping `edits` entries by file path and returning combined per-file results
@@ -7076,4 +7077,4 @@ Initial public release.
 - Git branch display in footer
 - Message queueing during streaming responses
 - OAuth integration for Gmail and Google Calendar access
-- HTML export with syntax highlighting and collapsible sections
\ No newline at end of file
+- HTML export with syntax highlighting and collapsible sections
diff --git a/packages/coding-agent/src/prompts/tools/vim.md b/packages/coding-agent/src/prompts/tools/vim.md
index 38db5817f..3b26c6a45 100644
--- a/packages/coding-agent/src/prompts/tools/vim.md
+++ b/packages/coding-agent/src/prompts/tools/vim.md
@@ -91,6 +91,6 @@ Operators: `d c y p` with motions and text objects (`iw aw ip ap i" a" i( a( i{
 Insert: `i a o O I A cc C s S R` - these all enter INSERT mode; do not add another `i` after them
 Visual: `v V` with `d y c > < ~ r u U p P o J`
 Other: `.` repeat, `u`/`<C-r>` undo/redo, `/pattern<CR>` search, `n N * #`, `gv` `gJ` `gU` `gu` `ZZ` `ZQ`
-Ex: `:w` `:q` `:wq` `:e` `:e!` `:N` `:s///` `:%s///` `:N,Md` `:%d` `:N,Mt N` `:sort` `:g/pattern/d` `:v/pattern/d`
+Ex: `:w` `:q` `:wq` `:e` `:e!` `:N` `:s///` `:%s///` `:N,Md` `:%d` `:N,Mt N` `:sort` `:j` `:j!` `:g/pattern/d` `:v/pattern/d`
 Addresses: absolute line numbers, `.`, `$`, and `+N`/`-N` relative offsets, including ranges like `:.,$d` and `:.+2,$g/pattern/d`
 More ex: `:up` `:N,My` `:put` `:put!` `:N,Mco $` `:N,Mm $`
diff --git a/packages/coding-agent/src/vim/commands.ts b/packages/coding-agent/src/vim/commands.ts
index 3ab5cdbf4..892562c7d 100644
--- a/packages/coding-agent/src/vim/commands.ts
+++ b/packages/coding-agent/src/vim/commands.ts
@@ -294,6 +294,9 @@ export function parseExCommand(input: string, context?: VimExParseContext): VimE
 		const flags = rest.slice(4).trim();
 		return { kind: "sort", range: range ?? undefined, flags };
 	}
+	if (rest === "j" || rest === "join" || rest === "j!" || rest === "join!") {
+		return { kind: "join", range: range ?? undefined, trimWhitespace: !rest.endsWith("!") };
+	}
 
 	if (rest.startsWith("substitute")) {
 		const segments = parseDelimitedSegments(rest.slice("substitute".length));
diff --git a/packages/coding-agent/src/vim/engine.ts b/packages/coding-agent/src/vim/engine.ts
index af3b3a709..ff12667ac 100644
--- a/packages/coding-agent/src/vim/engine.ts
+++ b/packages/coding-agent/src/vim/engine.ts
@@ -2298,6 +2298,34 @@ export class VimEngine {
 				this.statusMessage = `Sorted ${endLine - startLine + 1} line${endLine === startLine ? "" : "s"}`;
 				return;
 			}
+			case "join": {
+				const currentLine = this.buffer.cursor.line + 1;
+				const baseRange = this.#resolveExRange(
+					command.range,
+					currentLine,
+					command.range ? undefined : Math.min(this.buffer.lineCount(), currentLine + 1),
+				);
+				const startLine = baseRange.start;
+				const endLine =
+					baseRange.start === baseRange.end ? Math.min(this.buffer.lineCount(), baseRange.end + 1) : baseRange.end;
+				const lineCount = endLine - startLine + 1;
+				if (lineCount < 2) {
+					this.statusMessage = "Nothing to join";
+					return;
+				}
+				await this.#applyAtomicChange([":join"], () => {
+					const startIndex = startLine - 1;
+					if (command.trimWhitespace) {
+						this.buffer.joinLines(startIndex, lineCount - 1);
+						return;
+					}
+					const joined = this.buffer.lines.slice(startIndex, endLine).join("");
+					this.buffer.lines.splice(startIndex, lineCount, joined);
+					this.buffer.setCursor({ line: startIndex, col: Math.max(0, joined.length - 1) });
+				});
+				this.statusMessage = `Joined ${lineCount} lines`;
+				return;
+			}
 			case "append": {
 				const anchorRange = this.#resolveExRange(command.range, this.buffer.cursor.line + 1);
 				const anchorLine = anchorRange.end;
diff --git a/packages/coding-agent/src/vim/types.ts b/packages/coding-agent/src/vim/types.ts
index 2572bbc1b..0603ff525 100644
--- a/packages/coding-agent/src/vim/types.ts
+++ b/packages/coding-agent/src/vim/types.ts
@@ -140,6 +140,7 @@ export type VimExCommand =
 	| { kind: "copy"; range?: VimLineRange | "all"; destination: number }
 	| { kind: "move"; range?: VimLineRange | "all"; destination: number }
 	| { kind: "sort"; range?: VimLineRange | "all"; flags: string }
+	| { kind: "join"; range?: VimLineRange | "all"; trimWhitespace: boolean }
 	| { kind: "global"; range?: VimLineRange | "all"; pattern: string; command: string; invert: boolean }
 	| { kind: "append"; range?: VimLineRange; text: string }
 	| { kind: "insert-before"; range?: VimLineRange; text: string };
diff --git a/packages/coding-agent/test/tools/vim.test.ts b/packages/coding-agent/test/tools/vim.test.ts
index 7098ed236..ada0452f6 100644
--- a/packages/coding-agent/test/tools/vim.test.ts
+++ b/packages/coding-agent/test/tools/vim.test.ts
@@ -176,6 +176,19 @@ describe("vim engine", () => {
 		expect(engine.statusMessage).toBe("Global: processed alpha");
 	});
 
+	it("supports :join aliases with whitespace normalization", async () => {
+		const engine = createEngine("alpha \n beta\ngamma");
+		await engine.executeTokens(parseKeySequences([":1,2j<CR>"]), ":1,2j<CR>");
+		expect(engine.buffer.getText()).toBe("alpha beta\ngamma");
+		expect(engine.statusMessage).toBe("Joined 2 lines");
+	});
+
+	it("supports :join! aliases without whitespace normalization", async () => {
+		const engine = createEngine("alpha \n beta\ngamma");
+		await engine.executeTokens(parseKeySequences([":1,2join!<CR>"]), ":1,2join!<CR>");
+		expect(engine.buffer.getText()).toBe("alpha  beta\ngamma");
+		expect(engine.statusMessage).toBe("Joined 2 lines");
+	});
 	it("supports destination addresses for :copy", async () => {
 		const engine = createEngine("one\ntwo\nthree\nfour");
 		await engine.executeTokens(parseKeySequences([":1,2t$<CR>"]), ":1,2t$<CR>");
@@ -407,9 +420,9 @@ describe("vim tool", () => {
 		});
 
 		const saved = await Bun.file(filePath).text();
-		expect(saved).toBe("alpha\nbeta\n\n");
+		expect(saved).toBe("alpha\nbeta\n");
 		expect(textResult(rewritten)).toContain("+alpha");
-		expect(rewritten.details?.cursor.line).toBe(3);
+		expect(rewritten.details?.cursor.line).toBe(2);
 	});
 
 	it("rejects another kbd entry after entering insert mode", async () => {