diff --git a/src/main.rs b/src/main.rs
index 0112a4e..7f49f53 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -92,6 +92,8 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     // 2. Build 'Desired' State (Map<RepoName, CloneUrl>)
     info!("Resolving desired state from configuration...");
     let mut desired_repos: HashMap<String, String> = HashMap::new();
+    let mut seen_names: HashSet<String> = HashSet::new();
+    let mut has_error = false;
 
     // 2a. Static Repos
     if let Some(repos) = &config.repos {
@@ -101,6 +103,18 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                 .as_deref()
                 .or_else(|| extract_repo_name(&r.url))
                 .ok_or_else(|| format!("Invalid URL: {}", r.url))?;
+
+            let name_lower = name.to_lowercase();
+            if seen_names.contains(&name_lower) {
+                warn!(
+                    "Duplicate repository name detected (case-insensitive): '{}'. URL: {}",
+                    name, r.url
+                );
+                has_error = true;
+                continue;
+            }
+            seen_names.insert(name_lower);
+
             desired_repos.insert(name.to_string(), r.url.clone());
         }
     }
@@ -113,12 +127,26 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                 fetch_external_org_repos(&http_client, &org.url, org.api_key.as_deref()).await?;
             for url in urls {
                 if let Some(name) = extract_repo_name(&url) {
+                    let name_lower = name.to_lowercase();
+                    if seen_names.contains(&name_lower) {
+                        warn!(
+                            "Duplicate repository name detected (case-insensitive) from organization import: '{}'. URL: {}",
+                            name, url
+                        );
+                        has_error = true;
+                        continue;
+                    }
+                    seen_names.insert(name_lower);
                     desired_repos.insert(name.to_string(), url);
                 }
             }
         }
     }
 
+    if has_error {
+        return Err("Duplicate repository names detected. Please fix the configuration.".into());
+    }
+
     // 3. Build 'Current' State (Set<RepoName>)
     info!("Fetching existing repositories from Gitea ({})", owner_name);
     let existing_repos =
diff --git a/vibe_coding_log/session_2026_01_10_duplicate_detection.md b/vibe_coding_log/session_2026_01_10_duplicate_detection.md
new file mode 100644
index 0000000..c47d43a
--- /dev/null
+++ b/vibe_coding_log/session_2026_01_10_duplicate_detection.md
@@ -0,0 +1,23 @@
+# Session 2026-01-10: Duplicate Repository Detection
+
+*   **Date**: 2026-01-10
+*   **Model**: Gemini 2.5 Flash / Gemini 3 Pro Preview
+*   **Goal**: Implement case-insensitive duplication detection for repository names in the configuration.
+*   **Outcome**: Added logic to detect duplicate repository names (case-insensitive) from both static configuration and organization imports. The tool now logs warnings for all detected duplicates and then exits with a fatal error if any duplicates were found.
+
+## Details
+
+1.  **Duplicate Detection**:
+    *   Modified `src/main.rs` to maintain a `HashSet` of lowercased repository names.
+    *   Checks both the `repos` list and `organizations` imports.
+    *   If a duplicate is found, a `WARN` log is emitted with details (name and URL).
+    *   A `has_error` flag is set to true.
+
+2.  **Error Handling**:
+    *   After processing all sources, if `has_error` is true, the program returns a fatal error: "Duplicate repository names detected. Please fix the configuration."
+    *   This ensures the user sees all conflicts before the program exits.
+
+## Testing
+
+*   Created a `duplicate_repro.toml` with conflicting names (e.g., `ProjectA` vs `projecta`).
+*   Verified that `cargo run -- --config duplicate_repro.toml --dry-run` correctly outputted warnings for each duplicate and then exited with a non-zero status code and the expected error message.