diff --git a/lib/std/core/array.c3 b/lib/std/core/array.c3
index 6ca1d501e..abb808e34 100644
--- a/lib/std/core/array.c3
+++ b/lib/std/core/array.c3
@@ -79,7 +79,7 @@ macro concat(arr1, arr2, Allocator allocator) @nodiscard
  @require @typekind(arr1) == SLICE || @typekind(arr1) == ARRAY
  @require @typekind(arr2) == SLICE || @typekind(arr2) == ARRAY
  @require @typeis(arr1[0], $typeof(arr2[0])) "Arrays must have the same type"
- @ensure result.len == arr1.len + arr2.len
+ @ensure return.len == arr1.len + arr2.len
 *>
 macro concat_new(arr1, arr2, Allocator allocator = allocator::heap()) @nodiscard
 {
@@ -95,7 +95,7 @@ macro concat_new(arr1, arr2, Allocator allocator = allocator::heap()) @nodiscard
  @require @typekind(arr1) == SLICE || @typekind(arr1) == ARRAY
  @require @typekind(arr2) == SLICE || @typekind(arr2) == ARRAY
  @require @typeis(arr1[0], $typeof(arr2[0])) "Arrays must have the same type"
- @ensure result.len == arr1.len + arr2.len
+ @ensure return.len == arr1.len + arr2.len
 *>
 macro tconcat(arr1, arr2) @nodiscard => concat(arr1, arr2, allocator::temp());
 
diff --git a/releasenotes.md b/releasenotes.md
index 99e124a60..f4d89707e 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -25,6 +25,7 @@
 - Deprecate `fn void! main() type main functions.
 - Deprecate old `void!` @benchmark and @test functions.
 - Allow test runners to take String[] arguments.
+- Added `--lsp` output.
 
 ### Fixes
 - Fix case trying to initialize a `char[*]*` from a String.
diff --git a/src/build/build.h b/src/build/build.h
index b7af75318..d1437c885 100644
--- a/src/build/build.h
+++ b/src/build/build.h
@@ -491,6 +491,7 @@ typedef struct BuildOptions_
 	bool emit_asm;
 	bool benchmark_mode;
 	bool test_mode;
+	bool lsp_mode;
 	bool no_entry;
 	bool no_obj;
 	bool no_headers;
@@ -600,6 +601,7 @@ typedef struct
 	bool generate_test_runner;
 	bool benchmark_output;
 	bool test_output;
+	bool lsp_output;
 	bool output_headers;
 	bool output_ast;
 	bool lex_only;
diff --git a/src/build/build_options.c b/src/build/build_options.c
index 0b559982c..66e053e6a 100644
--- a/src/build/build_options.c
+++ b/src/build/build_options.c
@@ -125,7 +125,9 @@ static void usage(bool full)
 		PRINTF("  --optsize=<option>         - Code size optimization: none, small, tiny.");
 		PRINTF("  --single-module=<yes|no>   - Compile all modules together, enables more inlining.");
 		PRINTF("  --show-backtrace=<yes|no>  - Show detailed backtrace on segfaults.");
+		PRINTF("  --lsp                      - Emit data about errors suitable for a LSP.");
 		PRINTF("  --old-test-bench=<yes|no>  - Allow benchmarks and tests to use the deprecated 'void!' returns.");
+
 	}
 	PRINTF("");
 	PRINTF("  -g                         - Emit debug info.");
@@ -1082,8 +1084,16 @@ static void parse_option(BuildOptions *options)
 				options->benchmark_mode = true;
 				return;
 			}
+			if (match_longopt("lsp"))
+			{
+				options->lsp_mode = true;
+				options->strip_unused = STRIP_UNUSED_OFF;
+				options->test_mode = false;
+				return;
+			}
 			if (match_longopt("test"))
 			{
+				options->lsp_mode = false;
 				options->test_mode = true;
 				options->strip_unused = STRIP_UNUSED_OFF;
 				return;
diff --git a/src/build/builder.c b/src/build/builder.c
index b3c04a48c..6dac9e635 100644
--- a/src/build/builder.c
+++ b/src/build/builder.c
@@ -491,6 +491,13 @@ static void update_build_target_from_options(BuildTarget *target, BuildOptions *
 		target->emit_asm = false;
 		target->emit_object_files = false;
 	}
+	if (options->lsp_mode)
+	{
+		target->lsp_output = true;
+		target->emit_llvm = false;
+		target->emit_asm = false;
+		target->emit_object_files = false;
+	}
 	if (options->test_mode)
 	{
 		target->test_output = true;
diff --git a/src/compiler/compiler.c b/src/compiler/compiler.c
index 8f7436d19..49fd0224f 100644
--- a/src/compiler/compiler.c
+++ b/src/compiler/compiler.c
@@ -402,7 +402,16 @@ static void create_output_dir(const char *dir)
 
 void compiler_compile(void)
 {
+	if (compiler.build.lsp_output)
+	{
+		eprintf("> BEGINLSP\n");
+	}
 	sema_analysis_run();
+	if (compiler.build.lsp_output)
+	{
+		eprintf("< ENDLSP-OK\n");
+		exit_compiler(0);
+	}
 	compiler_sema_time = bench_mark();
 	Module **modules = compiler.context.module_list;
 	unsigned module_count = vec_size(modules);
@@ -437,7 +446,7 @@ void compiler_compile(void)
 			error_exit("Failed to create build directory '%s'.", compiler.build.build_dir);
 		}
 	}
-	if (compiler.build.ir_file_dir && (compiler.build.emit_llvm || compiler.build.test_output))
+	if (compiler.build.ir_file_dir && (compiler.build.emit_llvm || compiler.build.test_output || compiler.build.lsp_output))
 	{
 		if (!file_exists(compiler.build.ir_file_dir) && !dir_make(compiler.build.ir_file_dir))
 		{
diff --git a/src/compiler/diagnostics.c b/src/compiler/diagnostics.c
index 0b1aeea95..c78e6d80e 100644
--- a/src/compiler/diagnostics.c
+++ b/src/compiler/diagnostics.c
@@ -11,6 +11,38 @@
 #define LINES_SHOWN 4
 #define MAX_WIDTH 120
 
+static void eprint_escaped_string(const char *message)
+{
+	fputc('"', stderr);
+	char c;
+	while ((c = *(message++)) != 0)
+	{
+		switch (c)
+		{
+			case '\t':
+				fputs("\\t", stderr);
+				break;
+			case '\r':
+				break;
+			case '|':
+				fputs("\\x7c", stderr);
+				break;
+			case '\"':
+				fputs("\\\"", stderr);
+				break;
+			case '\\':
+				fputs("\\\\", stderr);
+				break;
+			case '\n':
+				fputs("\\n", stderr);
+				break;
+			default:
+				fputc(c, stderr);
+		}
+	}
+	fputc('"', stderr);
+}
+
 static void print_error_type_at(SourceSpan location, const char *message, PrintType print_type)
 {
 	if (!location.a)
@@ -19,7 +51,31 @@ static void print_error_type_at(SourceSpan location, const char *message, PrintT
 		return;
 	}
 	File *file = source_file_by_id(location.file_id);
-	if (compiler.build.test_output || compiler.build.benchmark_output)
+	if (compiler.build.lsp_output)
+	{
+		eprintf("> LSPERR|");
+		switch (print_type)
+		{
+			case PRINT_TYPE_ERROR:
+				eprintf("error");
+				break;
+			case PRINT_TYPE_NOTE:
+				eprintf("note");
+				break;
+			case PRINT_TYPE_WARN:
+				eprintf("warn");
+				break;
+			default:
+				UNREACHABLE
+		}
+		eprintf("|");
+		eprint_escaped_string(file->full_path);
+		eprintf("|%d|%d|", location.row, location.col);
+		eprint_escaped_string(message);
+		eprintf("\n");
+		return;
+	}
+	else if (compiler.build.test_output || compiler.build.benchmark_output)
 	{
 		switch (print_type)
 		{
diff --git a/src/compiler/semantic_analyser.c b/src/compiler/semantic_analyser.c
index aa01bfe72..3aab6d6a3 100644
--- a/src/compiler/semantic_analyser.c
+++ b/src/compiler/semantic_analyser.c
@@ -133,7 +133,15 @@ void context_pop_defers_and_replace_ast(SemaContext *context, Ast *ast)
 
 static inline void halt_on_error(void)
 {
-	if (compiler.context.errors_found > 0) exit_compiler(EXIT_FAILURE);
+	if (compiler.context.errors_found > 0)
+	{
+		if (compiler.build.lsp_output)
+		{
+			eprintf("> ENDLSP-ERROR\n");
+			exit_compiler(COMPILER_SUCCESS_EXIT);
+		}
+		exit_compiler(EXIT_FAILURE);
+	}
 }
 
 void sema_analyze_stage(Module *module, AnalysisStage stage)