diff --git a/CHANGELOG.md b/CHANGELOG.md
index bee197b..b30dff5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,12 @@ CalVer image tags (`stable-YYYY.MM.N`, `dev-YYYY.MM.N`) are produced for every C
 
 ## [Unreleased]
 
+### Added
+- `agnes query --json` is now a shortcut for `--format json` — paste-prompts and LLM-assisted analysts routinely reach for `--json` first, and the typer "Did you mean `--stdin`?" suggestion the missing flag previously produced was actively misleading. `--json --format <other>` is rejected as mutually exclusive (`--json --format json` is redundantly allowed). Closes #345 D.
+
+### Internal
+- Added explicit 5xx-path regression test alongside the existing 4xx case for `agnes query --remote` to lock in the `raise typer.Exit(1)` rc=1 contract for any non-2xx response (`tests/test_cli_query.py::test_remote_query_5xx_exits_nonzero`). No code change — the existing exit-code logic already does the right thing; the test guards against future regression. Closes #345 C.
+
 ### Fixed
 - **UI consistency pass** (I-UI-01..05): radio-card selected state on `/admin/tables` (14 cards get blue border + light bg highlight via `.sync-option-card:has(input:checked)`); promoted `.label-qualifier` / `.optional` to global rule (drops local duplicate); inline `<code>` migrated to design tokens with bg + border; `.btn-google` hover hardcoded swatches replaced with vars; `.code-block code` border + radius reset for dark containers; `.form-textarea` promoted to global. Plus #340 follow-up: removed leftover Phase F2 `{% if data_source_type == 'keboola' %}` guard around edit-modal JS so handlers ship to every instance type (Discover button onclick call sites still respect the guard). Closes #347 (credit @MonikaFeigler).
 - `agnes refresh-marketplace` (non-bootstrap path) now re-applies
diff --git a/cli/commands/query.py b/cli/commands/query.py
index 3a455aa..bee82dd 100644
--- a/cli/commands/query.py
+++ b/cli/commands/query.py
@@ -15,10 +15,24 @@ def query_command(
     sql_opt: Optional[str] = typer.Option(None, "--sql", help="SQL query to execute (named option)"),
     remote: bool = typer.Option(False, "--remote", help="Execute on server instead of locally"),
     fmt: str = typer.Option("table", "--format", "-f", help="Output format: table, json, csv"),
+    json_flag: bool = typer.Option(False, "--json", help="Shortcut for --format json"),
     limit: int = typer.Option(1000, "--limit", help="Max rows to return"),
     stdin: bool = typer.Option(False, "--stdin", help="Read SQL from stdin as JSON {\"sql\": \"...\"}"),
 ):
     """Execute SQL query against DuckDB."""
+    # `--json` is an alias for `--format json` (issue #345 D). Paste-prompts
+    # and LLM-assisted analysis routinely reach for `--json`; the typer
+    # "Did you mean --stdin?" suggestion that the absence of this flag
+    # produced was actively misleading.
+    if json_flag:
+        if fmt != "table" and fmt != "json":
+            typer.echo(
+                f"Error: --json and --format={fmt} are mutually exclusive.",
+                err=True,
+            )
+            raise typer.Exit(1)
+        fmt = "json"
+
     # Resolve SQL from exactly one of: positional, --sql, or --stdin
     sources_provided = sum([
         sql is not None,
diff --git a/tests/test_cli_query.py b/tests/test_cli_query.py
index db9fe51..709c655 100644
--- a/tests/test_cli_query.py
+++ b/tests/test_cli_query.py
@@ -47,6 +47,51 @@ class TestRemoteQuery:
         assert "HTTP 400" in result.output
         assert "bad SQL" in result.output
 
+    def test_remote_query_5xx_exits_nonzero(self):
+        """5xx server errors propagate to a nonzero exit code (issue #345 C).
+
+        Without this, ``set -e`` shells, CI pipelines, and any wrapper
+        script that checks ``$?`` to detect failure would silently
+        proceed even when the server returned ``HTTP 502:`` to stdout.
+        The reporter who filed #345 hit the exact rc=0-on-502 pattern
+        on a slightly older CLI build; this guards against any future
+        regression that drops the ``raise typer.Exit(1)`` from the
+        non-200 branch of ``_query_remote``.
+        """
+        with patch("cli.client.api_post", return_value=_resp(502, text="bad gateway")):
+            result = runner.invoke(app, ["query", "SELECT 1", "--remote"])
+        assert result.exit_code != 0, (
+            f"Expected nonzero exit for HTTP 502, got rc={result.exit_code}. "
+            f"Output: {result.output}"
+        )
+        assert "HTTP 502" in result.output
+
+    def test_remote_query_json_alias_equals_format_json(self):
+        """``--json`` is a shortcut for ``--format json`` (issue #345 D).
+
+        Paste-prompts and LLM-assisted analysts routinely reach for
+        ``agnes query --json`` first; the typer "Did you mean --stdin?"
+        suggestion the absence of this flag previously produced was
+        actively misleading.
+        """
+        payload = {"columns": ["id"], "rows": [[1]], "truncated": False}
+        with patch("cli.client.api_post", return_value=_resp(200, payload)):
+            result = runner.invoke(app, ["query", "SELECT 1", "--remote", "--json"])
+        assert result.exit_code == 0
+        # Output is parseable JSON, equivalent to --format json
+        parsed = json.loads(result.output.strip())
+        assert parsed == [{"id": 1}]
+
+    def test_json_and_explicit_csv_format_are_mutually_exclusive(self):
+        """``--json --format csv`` is contradictory; reject with rc=1.
+
+        ``--json --format json`` is allowed (redundant but consistent);
+        ``--json`` alone is the common case.
+        """
+        result = runner.invoke(app, ["query", "SELECT 1", "--json", "--format", "csv"])
+        assert result.exit_code == 1
+        assert "mutually exclusive" in result.output
+
     def test_remote_query_truncated(self):
         """Truncated result shows warning."""
         payload = {"columns": ["id"], "rows": [[i] for i in range(5)], "truncated": True}