diff --git a/.changeset/fix-cli-validation.md b/.changeset/fix-cli-validation.md
new file mode 100644
index 0000000..4920343
--- /dev/null
+++ b/.changeset/fix-cli-validation.md
@@ -0,0 +1,5 @@
+---
+"@satoshai/abi-cli": patch
+---
+
+Add CLI validation for --output/--stdout with multiple contracts and improve fetch error messages
diff --git a/src/commands/fetch.ts b/src/commands/fetch.ts
index d03a7a0..528081d 100644
--- a/src/commands/fetch.ts
+++ b/src/commands/fetch.ts
@@ -50,6 +50,18 @@ export const fetchCommand = defineCommand({
 
     const contractIds = args.contract.split(',').map((s) => s.trim());
 
+    if (args.output && contractIds.length > 1) {
+      throw new Error(
+        '--output cannot be used with multiple contracts. Omit --output to write separate files, or use --stdout.',
+      );
+    }
+
+    if (args.stdout && contractIds.length > 1) {
+      throw new Error(
+        '--stdout cannot be used with multiple contracts. Fetch one contract at a time with --stdout.',
+      );
+    }
+
     for (const contractId of contractIds) {
       const { address, name } = parseContractId(contractId);
 
diff --git a/src/fetcher.ts b/src/fetcher.ts
index 18a1523..18de543 100644
--- a/src/fetcher.ts
+++ b/src/fetcher.ts
@@ -31,7 +31,15 @@ export async function fetchContractAbi(
   const baseUrl = resolveNetwork(network);
   const url = `${baseUrl}/v2/contracts/interface/${address}/${name}`;
 
-  const response = await fetch(url);
+  let response: Response;
+  try {
+    response = await fetch(url);
+  } catch (cause) {
+    throw new Error(
+      `Network error fetching ABI for ${address}.${name} on ${network}`,
+      { cause },
+    );
+  }
 
   if (!response.ok) {
     if (response.status === 404) {
@@ -44,5 +52,12 @@ export async function fetchContractAbi(
     );
   }
 
-  return (await response.json()) as ClarityAbi;
+  try {
+    return (await response.json()) as ClarityAbi;
+  } catch (cause) {
+    throw new Error(
+      `Invalid JSON response for ${address}.${name} on ${network}`,
+      { cause },
+    );
+  }
 }