diff --git a/crates/pinakes-plugin-api/Cargo.toml b/crates/pinakes-plugin-api/Cargo.toml
index 94f529a..bfc8dd4 100644
--- a/crates/pinakes-plugin-api/Cargo.toml
+++ b/crates/pinakes-plugin-api/Cargo.toml
@@ -10,6 +10,7 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 thiserror = { workspace = true }
 async-trait = { workspace = true }
+tracing = { workspace = true }
 
 # For plugin manifest parsing
 toml = { workspace = true }
diff --git a/crates/pinakes-plugin-api/src/manifest.rs b/crates/pinakes-plugin-api/src/manifest.rs
index 49c5748..340dc24 100644
--- a/crates/pinakes-plugin-api/src/manifest.rs
+++ b/crates/pinakes-plugin-api/src/manifest.rs
@@ -40,6 +40,33 @@ pub struct UiSection {
   /// Widgets to inject into existing host pages
   #[serde(default)]
   pub widgets: Vec<UiWidget>,
+
+  /// API endpoint paths this plugin's UI requires.
+  /// Each must start with `/api/`. Informational; host may check availability.
+  #[serde(default, skip_serializing_if = "Vec::is_empty")]
+  pub required_endpoints: Vec<String>,
+
+  /// CSS custom property overrides provided by this plugin.
+  /// Keys are property names (e.g. `--accent-color`), values are CSS values.
+  /// The host applies these to `document.documentElement` on startup.
+  #[serde(default, skip_serializing_if = "HashMap::is_empty")]
+  pub theme_extensions: HashMap<String, String>,
+}
+
+impl UiSection {
+  /// Validate that all declared required endpoints start with `/api/`.
+  ///
+  /// # Errors
+  ///
+  /// Returns an error string for the first invalid endpoint found.
+  pub fn validate(&self) -> Result<(), String> {
+    for ep in &self.required_endpoints {
+      if !ep.starts_with("/api/") {
+        return Err(format!("required_endpoint must start with '/api/': {ep}"));
+      }
+    }
+    Ok(())
+  }
 }
 
 /// Entry for a UI page in the manifest - can be inline or file reference
@@ -267,6 +294,15 @@ impl PluginManifest {
       ));
     }
 
+    // Validate UI section (required_endpoints format); non-fatal: warn only
+    if let Err(e) = self.ui.validate() {
+      tracing::warn!(
+        plugin = %self.plugin.name,
+        error = %e,
+        "plugin UI section has invalid required_endpoints"
+      );
+    }
+
     // Validate UI pages
     for (idx, page_entry) in self.ui.pages.iter().enumerate() {
       match page_entry {
@@ -663,4 +699,89 @@ gap = 16
     let manifest = PluginManifest::parse_str(toml).unwrap();
     assert_eq!(manifest.ui.pages.len(), 2);
   }
+
+  #[test]
+  fn test_ui_section_validate_accepts_api_paths() {
+    let section = UiSection {
+      pages:              vec![],
+      widgets:            vec![],
+      required_endpoints: vec![
+        "/api/v1/media".to_string(),
+        "/api/plugins/my-plugin/data".to_string(),
+      ],
+      theme_extensions:   HashMap::new(),
+    };
+    assert!(section.validate().is_ok());
+  }
+
+  #[test]
+  fn test_ui_section_validate_rejects_non_api_path() {
+    let section = UiSection {
+      pages:              vec![],
+      widgets:            vec![],
+      required_endpoints: vec!["/not-api/something".to_string()],
+      theme_extensions:   HashMap::new(),
+    };
+    assert!(section.validate().is_err());
+  }
+
+  #[test]
+  fn test_ui_section_validate_rejects_empty_sections_with_bad_path() {
+    let section = UiSection {
+      pages:              vec![],
+      widgets:            vec![],
+      required_endpoints: vec!["/api/ok".to_string(), "no-slash".to_string()],
+      theme_extensions:   HashMap::new(),
+    };
+    let err = section.validate().unwrap_err();
+    assert!(
+      err.contains("no-slash"),
+      "error should mention the bad endpoint"
+    );
+  }
+
+  #[test]
+  fn test_theme_extensions_roundtrip() {
+    let toml = r##"
+[plugin]
+name = "theme-plugin"
+version = "1.0.0"
+api_version = "1.0"
+kind = ["theme_provider"]
+
+[plugin.binary]
+wasm = "plugin.wasm"
+
+[ui.theme_extensions]
+"--accent-color" = "#ff6b6b"
+"--sidebar-width" = "280px"
+"##;
+
+    let manifest = PluginManifest::parse_str(toml).unwrap();
+    assert_eq!(
+      manifest.ui.theme_extensions.get("--accent-color").map(String::as_str),
+      Some("#ff6b6b")
+    );
+    assert_eq!(
+      manifest.ui.theme_extensions.get("--sidebar-width").map(String::as_str),
+      Some("280px")
+    );
+  }
+
+  #[test]
+  fn test_theme_extensions_empty_by_default() {
+    let toml = r#"
+[plugin]
+name = "no-theme"
+version = "1.0.0"
+api_version = "1.0"
+kind = ["media_type"]
+
+[plugin.binary]
+wasm = "plugin.wasm"
+"#;
+
+    let manifest = PluginManifest::parse_str(toml).unwrap();
+    assert!(manifest.ui.theme_extensions.is_empty());
+  }
 }