bcc.py

@@ -2309,8 +2309,13 @@ class MainWindow(QMainWindow):
             self.validation_lbl.setStyleSheet(f"color: {WARN};")
             self.save_btn.setEnabled(False)
             return False
-        self.validation_lbl.setText("✓ valid")
-        self.validation_lbl.setStyleSheet(f"color: {GOOD};")
+        lint_warnings = core.lint_servers(self.servers)
+        if lint_warnings:
+            self.validation_lbl.setText(f"⚠ {lint_warnings[0]}")
+            self.validation_lbl.setStyleSheet(f"color: {WARN};")
+        else:
+            self.validation_lbl.setText("✓ valid")
+            self.validation_lbl.setStyleSheet(f"color: {GOOD};")
         self.save_btn.setEnabled(self.dirty)
         return True
 

bcc_core.py

@@ -1213,6 +1213,63 @@ def validate_servers(servers: list[ServerEntry]) -> list[str]:
     return problems
 
 
+def lint_server(name: str, data: dict) -> list[str]:
+    """Return non-blocking structural warnings for a single server definition.
+
+    Unlike validate_servers, nothing here blocks Save -- these are advisory
+    notes about shapes that will round-trip through JSON fine but are
+    probably not what the user intended (args given as a plain string
+    instead of a list, an env value that isn't a string, an unrecognized
+    `type`, unknown top-level fields, etc.).
+    """
+    nm = name.strip() or "(unnamed)"
+    warnings: list[str] = []
+
+    if "command" in data and not isinstance(data["command"], str):
+        warnings.append(f"'{nm}': 'command' should be a string")
+
+    if "args" in data:
+        args = data["args"]
+        if not isinstance(args, list):
+            warnings.append(f"'{nm}': 'args' should be a list (one argument per item)")
+        elif any(not isinstance(a, str) for a in args):
+            warnings.append(
+                f"'{nm}': 'args' contains non-string values "
+                "(they will be saved as-is; Claude expects strings)"
+            )
+
+    for field in ("env", "headers"):
+        if field not in data:
+            continue
+        val = data[field]
+        if not isinstance(val, dict):
+            warnings.append(f"'{nm}': '{field}' should be an object of string key/value pairs")
+        elif any(not isinstance(v, str) for v in val.values()):
+            warnings.append(
+                f"'{nm}': '{field}' contains non-string values "
+                "(they will be saved as-is; Claude expects strings)"
+            )
+
+    if "type" in data:
+        t = data["type"]
+        if t not in ("http", "sse", "stdio"):
+            warnings.append(f"'{nm}': 'type' should be one of http, sse, stdio (found {t!r})")
+
+    extra = sorted(k for k in data if k not in KNOWN_FIELDS)
+    if extra:
+        warnings.append(f"'{nm}': extra fields preserved as-is: {', '.join(extra)}")
+
+    return warnings
+
+
+def lint_servers(servers: list[ServerEntry]) -> list[str]:
+    """Concatenate lint_server warnings across every entry, in order."""
+    out: list[str] = []
+    for s in servers:
+        out.extend(lint_server(s.name, s.data))
+    return out
+
+
 # --------------------------------------------------------------------------- #
 # Search / filter
 # --------------------------------------------------------------------------- #

tests/test_core.py

@@ -181,6 +181,85 @@ def test_valid_set_passes_clean():
     assert c.validate_servers([c.ServerEntry("good", {"command": "node"}, True)]) == []
 
 
+# --------------------------------------------------------------------------- #
+# 4b. Lint: non-blocking structural warnings
+# --------------------------------------------------------------------------- #
+def test_lint_flags_non_string_command():
+    warnings = c.lint_server("x", {"command": 5})
+    assert any("'command' should be a string" in w for w in warnings)
+
+
+def test_lint_flags_args_not_a_list():
+    warnings = c.lint_server("x", {"command": "node", "args": "-y foo"})
+    assert any("'args' should be a list" in w for w in warnings)
+
+
+def test_lint_flags_args_with_non_string_items():
+    warnings = c.lint_server("x", {"command": "node", "args": ["-y", 5]})
+    assert any("'args' contains non-string values" in w for w in warnings)
+
+
+def test_lint_flags_env_not_a_dict():
+    warnings = c.lint_server("x", {"command": "node", "env": ["FOO=bar"]})
+    assert any("'env' should be an object" in w for w in warnings)
+
+
+def test_lint_flags_env_with_non_string_values():
+    warnings = c.lint_server("x", {"command": "node", "env": {"FOO": 5}})
+    assert any("'env' contains non-string values" in w for w in warnings)
+
+
+def test_lint_flags_headers_not_a_dict():
+    warnings = c.lint_server("x", {"url": "https://x", "headers": ["Authorization: x"]})
+    assert any("'headers' should be an object" in w for w in warnings)
+
+
+def test_lint_flags_headers_with_non_string_values():
+    warnings = c.lint_server("x", {"url": "https://x", "headers": {"Authorization": 5}})
+    assert any("'headers' contains non-string values" in w for w in warnings)
+
+
+def test_lint_flags_bad_type_value():
+    warnings = c.lint_server("x", {"url": "https://x", "type": "websocket"})
+    assert any("'type'" in w and "websocket" in w for w in warnings)
+
+
+def test_lint_flags_extra_unknown_fields():
+    warnings = c.lint_server("x", {"command": "node", "cwd": "/tmp", "timeout": 30})
+    matches = [w for w in warnings if "extra fields preserved as-is" in w]
+    assert len(matches) == 1
+    assert "cwd" in matches[0]
+    assert "timeout" in matches[0]
+
+
+def test_lint_clean_server_yields_no_warnings():
+    assert c.lint_server("good", {"command": "node", "args": ["a.js"]}) == []
+    assert (
+        c.lint_server(
+            "remote", {"url": "https://x", "type": "http", "headers": {"Authorization": "x"}}
+        )
+        == []
+    )
+
+
+def test_lint_servers_aggregates_across_entries():
+    entries = [
+        c.ServerEntry("a", {"command": 5}, True),
+        c.ServerEntry("b", {"url": "https://x", "type": "bogus"}, True),
+    ]
+    warnings = c.lint_servers(entries)
+    assert any("'a'" in w and "'command' should be a string" in w for w in warnings)
+    assert any("'b'" in w and "'type'" in w for w in warnings)
+
+
+def test_lint_warning_is_not_a_blocking_problem():
+    # args given as a single string isn't caught by validate_servers (a
+    # command is still present), but it's a lint warning.
+    entry = c.ServerEntry("x", {"command": "node", "args": "-y foo"}, True)
+    assert c.validate_servers([entry]) == []
+    assert c.lint_servers([entry]) != []
+
+
 # --------------------------------------------------------------------------- #
 # 5. Secrets: detection + redaction
 # --------------------------------------------------------------------------- #