diff --git a/docs/interface/flow-editor.md b/docs/interface/flow-editor.md
index cc40063..102b0c5 100644
--- a/docs/interface/flow-editor.md
+++ b/docs/interface/flow-editor.md
@@ -57,7 +57,10 @@ renamed.
 **Settings** is generated from the node type's parameter schema, so an MQTT
 node shows broker, topic and QoS, and an ntfy node shows server, topic and
 priority. A field marked as a credential renders as a picker over your stored
-[secrets](operations.md) instead of a text box.
+[secrets](operations.md) instead of a text box. A setting holding JSON, such as
+a Switch node's rules, shows one line of it; click it to edit the whole value
+in a larger editor, which saves only once the text parses. Escape or Cancel
+leaves the setting as it was.
 
 A Function node gets a second settings section where you add your own: a
 setting is a constant of this node's code and arrives as an argument beside its
diff --git a/frontend/src/components/Flow/JsonField.tsx b/frontend/src/components/Flow/JsonField.tsx
new file mode 100644
index 0000000..6f3b68f
--- /dev/null
+++ b/frontend/src/components/Flow/JsonField.tsx
@@ -0,0 +1,125 @@
+import { Maximize2 } from "lucide-react"
+import { lazy, Suspense, useState } from "react"
+
+import { Button } from "@/components/ui/button"
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog"
+import { cn } from "@/lib/utils"
+
+const NodeEditor = lazy(() => import("./NodeEditor"))
+
+/** Why `text` is not JSON, or null when it is. */
+function parseError(text: string): string | null {
+  try {
+    JSON.parse(text)
+    return null
+  } catch (error) {
+    return (error as Error).message
+  }
+}
+
+/**
+ * A setting holding JSON: one line of it in the panel, the whole value in an
+ * editor a click away.
+ *
+ * The dialog edits a draft, so a half-typed value never reaches the node:
+ * Save stays off until the text parses.
+ */
+export function JsonField({
+  id,
+  value,
+  label,
+  className,
+  onChange,
+}: {
+  id?: string
+  value: unknown
+  /** The setting's name, which titles the dialog. */
+  label: string
+  className?: string
+  onChange: (next: unknown) => void
+}) {
+  // The text being edited; null while the dialog is shut.
+  const [draft, setDraft] = useState<string | null>(null)
+  const error = draft === null ? null : parseError(draft)
+
+  return (
+    <>
+      <button
+        type="button"
+        id={id}
+        aria-label={`Edit ${label}`}
+        data-testid="json-field"
+        className={cn(
+          "flex h-8 min-w-0 items-center gap-2 rounded-full border border-input bg-transparent px-3 text-left font-mono text-sm outline-none transition-[color,box-shadow] hover:bg-accent/50 focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 dark:bg-input/30",
+          className,
+        )}
+        onClick={() => setDraft(JSON.stringify(value, null, 2) ?? "")}
+      >
+        {/* No width of its own, so a long value never widens the panel. */}
+        <span className="w-0 flex-1 truncate">{JSON.stringify(value)}</span>
+        <Maximize2 className="size-3.5 shrink-0 text-muted-foreground" />
+      </button>
+
+      <Dialog
+        open={draft !== null}
+        onOpenChange={(open) => {
+          if (!open) setDraft(null)
+        }}
+      >
+        <DialogContent
+          data-testid="json-dialog"
+          className="flex h-[80dvh] flex-col sm:max-w-2xl"
+          // The editor takes the caret itself once it has loaded.
+          onOpenAutoFocus={(event) => event.preventDefault()}
+        >
+          <DialogHeader>
+            <DialogTitle className="font-mono">{label}</DialogTitle>
+            <DialogDescription>JSON</DialogDescription>
+          </DialogHeader>
+          <div className="min-h-0 flex-1 overflow-hidden rounded-md border border-border">
+            <Suspense
+              fallback={
+                <div className="h-full w-full animate-pulse bg-muted" />
+              }
+            >
+              <NodeEditor
+                language="json"
+                autoFocus
+                value={draft ?? ""}
+                onChange={setDraft}
+              />
+            </Suspense>
+          </div>
+          {error ? (
+            <p className="text-xs text-destructive" role="alert">
+              {error}
+            </p>
+          ) : null}
+          <DialogFooter>
+            <Button variant="outline" onClick={() => setDraft(null)}>
+              Cancel
+            </Button>
+            <Button
+              disabled={error !== null}
+              data-testid="json-save"
+              onClick={() => {
+                if (draft === null) return
+                onChange(JSON.parse(draft))
+                setDraft(null)
+              }}
+            >
+              Save
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+    </>
+  )
+}
diff --git a/frontend/src/components/Flow/NodeEditor.tsx b/frontend/src/components/Flow/NodeEditor.tsx
index 239845b..f0fc50f 100644
--- a/frontend/src/components/Flow/NodeEditor.tsx
+++ b/frontend/src/components/Flow/NodeEditor.tsx
@@ -6,19 +6,24 @@ import { Skeleton } from "@/components/ui/skeleton"
 import { monacoFontFamily, setupMonaco } from "./monacoSetup"
 
 /**
- * The embedded Python editor. Highlighting and bracket handling only: what the
- * code actually does is checked by the engine, which reports load and run
- * errors back onto the node.
+ * The embedded code editor, Python unless asked for JSON. Highlighting and
+ * bracket handling only: what the code actually does is checked by the engine,
+ * which reports load and run errors back onto the node.
  */
 export default function NodeEditor({
   value,
   onChange,
+  language = "python",
   readOnly = false,
+  autoFocus = false,
 }: {
   value: string
   onChange: (next: string) => void
+  language?: "python" | "json"
   /** Generated code: readable, and not this panel's to change. */
   readOnly?: boolean
+  /** Take the caret once mounted, as an editor opened on purpose should. */
+  autoFocus?: boolean
 }) {
   const { resolvedTheme } = useTheme()
   const [ready, setReady] = useState(false)
@@ -34,10 +39,11 @@ export default function NodeEditor({
 
   return (
     <Editor
-      language="python"
+      language={language}
       theme={resolvedTheme === "dark" ? "fluksio-dark" : "fluksio-light"}
       value={value}
       onChange={(next) => onChange(next ?? "")}
+      onMount={autoFocus ? (editor) => editor.focus() : undefined}
       loading={<Skeleton className="h-full w-full rounded-md" />}
       options={{
         readOnly,
diff --git a/frontend/src/components/Flow/NodePanel.tsx b/frontend/src/components/Flow/NodePanel.tsx
index 0115b90..6e5e206 100644
--- a/frontend/src/components/Flow/NodePanel.tsx
+++ b/frontend/src/components/Flow/NodePanel.tsx
@@ -46,6 +46,7 @@ import useCustomToast from "@/hooks/useCustomToast"
 import { inCodeEditor, useShortcuts } from "@/lib/shortcuts"
 import { cn } from "@/lib/utils"
 import { DtypeValue } from "./FlowBoundary"
+import { JsonField } from "./JsonField"
 import { MessageSparkline } from "./MessageSparkline"
 import {
   flavorsQueryOptions,
@@ -496,9 +497,10 @@ function castTo(type: FreeType, raw: string): unknown {
   if (type === "on/off") return raw === "true"
   if (type === "json") {
     try {
-      return JSON.parse(raw)
+      // An empty setting turned into JSON starts as an empty object.
+      return JSON.parse(raw || "{}")
     } catch {
-      // Half-typed JSON is normal while editing; keep the text until it parses.
+      // Text that is not JSON stays text, and the type select says so.
       return raw
     }
   }
@@ -615,6 +617,13 @@ function FreeParamsForm({
                   onChange({ ...params, [key]: checked })
                 }
               />
+            ) : type === "json" ? (
+              <JsonField
+                value={value}
+                label={key}
+                className="flex-1"
+                onChange={(next) => onChange({ ...params, [key]: next })}
+              />
             ) : (
               <Input
                 value={asText(value)}
@@ -891,8 +900,30 @@ function ParamsForm({
           )
         }
 
-        if (property.type === "object" || property.type === "array") {
-          return null
+        if (
+          property.type === "object" ||
+          property.type === "array" ||
+          (value !== null && typeof value === "object")
+        ) {
+          // An inject's per-port payloads are the fields drawn above.
+          if (type === "inject" && key === "payloads") return null
+          return (
+            <div key={key} className="grid gap-1.5">
+              <FieldLabel htmlFor={`param-${key}`} help={property.description}>
+                {label}
+              </FieldLabel>
+              <JsonField
+                id={`param-${key}`}
+                value={
+                  params[key] ??
+                  property.default ??
+                  (property.type === "array" ? [] : {})
+                }
+                label={label}
+                onChange={(next) => set(key, next)}
+              />
+            </div>
+          )
         }
 
         const numeric =
diff --git a/frontend/src/components/Flow/SidePanel.tsx b/frontend/src/components/Flow/SidePanel.tsx
index 9ff65b0..c2636ea 100644
--- a/frontend/src/components/Flow/SidePanel.tsx
+++ b/frontend/src/components/Flow/SidePanel.tsx
@@ -228,7 +228,9 @@ export function SidePanel({
   useEffect(() => {
     if (!open) return
     const onKey = (event: KeyboardEvent) => {
-      if (event.key === "Escape") onClose()
+      // A dialog opened from the panel closes on its own Escape and marks it
+      // handled; that one press should not take the panel with it.
+      if (event.key === "Escape" && !event.defaultPrevented) onClose()
     }
     window.addEventListener("keydown", onKey)
     return () => window.removeEventListener("keydown", onKey)
diff --git a/frontend/src/components/Flow/monacoSetup.ts b/frontend/src/components/Flow/monacoSetup.ts
index 13b440e..0276b54 100644
--- a/frontend/src/components/Flow/monacoSetup.ts
+++ b/frontend/src/components/Flow/monacoSetup.ts
@@ -1,15 +1,18 @@
 /**
  * Monaco, self-hosted and themed from the design tokens.
  *
- * Only the base editor and the Python grammar are pulled in; the other seventy
- * languages would triple the chunk for nothing. This module is imported by
- * NodeEditor alone, which the panel loads lazily.
+ * Only the base editor, the Python grammar and JSON (for settings holding JSON)
+ * are pulled in; the other seventy languages would triple the chunk for
+ * nothing. This module is imported by NodeEditor alone, which the panel loads
+ * lazily.
  */
 import { loader } from "@monaco-editor/react"
 import * as monaco from "monaco-editor/editor/editor.api"
 // Only Python registers itself; `basic-languages` would pull in all seventy.
 import "monaco-editor/languages/definitions/python/register"
+import "monaco-editor/languages/features/json/register"
 import editorWorker from "monaco-editor/editor/editor.worker?worker"
+import jsonWorker from "monaco-editor/languages/features/json/json.worker?worker"
 
 let configured = false
 
@@ -36,6 +39,11 @@ function defineThemes() {
         { token: "string", foreground: success.slice(1) },
         { token: "comment", foreground: muted.slice(1), fontStyle: "italic" },
         { token: "number", foreground: foreground.slice(1) },
+        // JSON names its tokens more specifically, so the base theme's
+        // colours would win over the generic ones above.
+        { token: "string.key.json", foreground: foreground.slice(1) },
+        { token: "string.value.json", foreground: success.slice(1) },
+        { token: "keyword.json", foreground: primary.slice(1) },
       ],
       colors: {
         "editor.background": background,
@@ -58,7 +66,10 @@ export function setupMonaco(): typeof monaco {
   configured = true
 
   // Self-hosted: no CDN fetch, so the editor works on a LAN install.
-  self.MonacoEnvironment = { getWorker: () => new editorWorker() }
+  self.MonacoEnvironment = {
+    getWorker: (_, label) =>
+      label === "json" ? new jsonWorker() : new editorWorker(),
+  }
   loader.config({ monaco })
   defineThemes()
   return monaco