diff --git a/packages/jupyterlab-lsp/schema/completion.json b/packages/jupyterlab-lsp/schema/completion.json
index 015857b5e..4e5e046e0 100644
--- a/packages/jupyterlab-lsp/schema/completion.json
+++ b/packages/jupyterlab-lsp/schema/completion.json
@@ -42,8 +42,13 @@
       "description": "The time to wait for the kernel completions suggestions in milliseconds. Set to 0 to disable kernel completions, or to -1 to wait indefinitely (not recommended)."
     },
     "disableCompletionsFrom": {
+      "title": "Disable completions by source",
       "description": "The sources from which to exclude completion from. Possible values include 'Kernel', 'LSP'.",
       "type": "array",
+      "items": {
+        "type": "string",
+        "enum": ["Kernel", "LSP"]
+      },
       "default": [],
       "uniqueItems": true
     },
@@ -62,6 +67,7 @@
     "kernelCompletionsFirst": {
       "title": "Prioritize completions from kernel",
       "default": false,
+      "type": "boolean",
       "description": "In case of ties when sorting completions, should the kernel completions receive higher priority than the language server completions?"
     },
     "caseSensitive": {
@@ -110,38 +116,36 @@
         "undefinitializer": "Constant",
         "base.devnull": "Constant"
       },
-      "patternProperties": {
-        "^.*$": {
-          "type": "string",
-          "enum": [
-            "Kernel",
-            "Text",
-            "Method",
-            "Function",
-            "Constructor",
-            "Field",
-            "Variable",
-            "Class",
-            "Interface",
-            "Module",
-            "Property",
-            "Unit",
-            "Value",
-            "Enum",
-            "Keyword",
-            "Snippet",
-            "Color",
-            "File",
-            "Reference",
-            "Folder",
-            "EnumMember",
-            "Constant",
-            "Struct",
-            "Event",
-            "Operator",
-            "TypeParameter"
-          ]
-        }
+      "additionalProperties": {
+        "type": "string",
+        "enum": [
+          "Kernel",
+          "Text",
+          "Method",
+          "Function",
+          "Constructor",
+          "Field",
+          "Variable",
+          "Class",
+          "Interface",
+          "Module",
+          "Property",
+          "Unit",
+          "Value",
+          "Enum",
+          "Keyword",
+          "Snippet",
+          "Color",
+          "File",
+          "Reference",
+          "Folder",
+          "EnumMember",
+          "Constant",
+          "Struct",
+          "Event",
+          "Operator",
+          "TypeParameter"
+        ]
       }
     },
     "disable": {
diff --git a/packages/jupyterlab-lsp/schema/highlights.json b/packages/jupyterlab-lsp/schema/highlights.json
index 444a06b80..139b6fbad 100644
--- a/packages/jupyterlab-lsp/schema/highlights.json
+++ b/packages/jupyterlab-lsp/schema/highlights.json
@@ -9,6 +9,7 @@
       "title": "Debouncer delay",
       "type": "number",
       "default": 250,
+      "minimum": 0,
       "description": "Number of milliseconds to delay sending out the highlights request to the language server; you can get better responsiveness adjusting this value, but setting it to zero can actually slow it down as the server might get overwhelmed when moving the cursor."
     },
     "removeOnBlur": {
diff --git a/packages/jupyterlab-lsp/schema/hover.json b/packages/jupyterlab-lsp/schema/hover.json
index 41c1bf207..91d29e9f3 100644
--- a/packages/jupyterlab-lsp/schema/hover.json
+++ b/packages/jupyterlab-lsp/schema/hover.json
@@ -16,12 +16,14 @@
       "title": "Throttler delay",
       "type": "number",
       "default": 50,
+      "minimum": 0,
       "description": "Number of milliseconds to delay sending out the hover request to the language server; you can get better responsiveness adjusting this value, but setting it to zero can actually slow it down as the server might get overwhelmed when moving the mouse over the code."
     },
     "cacheSize": {
       "title": "Cache size",
       "type": "number",
       "default": 25,
+      "minimum": 0,
       "description": "Up to how many hover responses should be cached at any given time. The cache being is invalidated after any change in the editor."
     },
     "disable": {
diff --git a/packages/jupyterlab-lsp/schema/plugin.json b/packages/jupyterlab-lsp/schema/plugin.json
index 7bbd7061f..30d8b2802 100644
--- a/packages/jupyterlab-lsp/schema/plugin.json
+++ b/packages/jupyterlab-lsp/schema/plugin.json
@@ -6,7 +6,6 @@
   "type": "object",
   "definitions": {
     "language-server": {
-      "title": "Language Server",
       "description": "Client and server configurations for a single language server",
       "type": "object",
       "default": {},
@@ -15,7 +14,8 @@
           "title": "Language Server Configurations",
           "description": "Configuration to be sent to language server over LSP when initialized: see the specific language server's documentation for more",
           "type": "object",
-          "default": {}
+          "default": {},
+          "additionalProperties": true
         },
         "priority": {
           "title": "Priority of the server",
diff --git a/packages/jupyterlab-lsp/schema/syntax_highlighting.json b/packages/jupyterlab-lsp/schema/syntax_highlighting.json
index 90645f4c4..20f7c54c2 100644
--- a/packages/jupyterlab-lsp/schema/syntax_highlighting.json
+++ b/packages/jupyterlab-lsp/schema/syntax_highlighting.json
@@ -9,6 +9,8 @@
       "title": "Threshold of foreign code coverage for changing the mode in an editor",
       "type": "number",
       "default": 0.5,
+      "minimum": 0,
+      "maximum": 1,
       "description": "If a code editor includes a code fragment in another language (for example a %%markdown magic in IPython) with appropriate foreign code extractor defined, and the extend of this code (coverage of the editor) passes the threshold, the syntax highlighting (i.e. the mode) will change to provide highlighting for the language of the foreign code."
     },
     "disable": {