diff --git a/src/converters/claude-to-opencode.ts b/src/converters/claude-to-opencode.ts
index ff6b31f..feea6cb 100644
--- a/src/converters/claude-to-opencode.ts
+++ b/src/converters/claude-to-opencode.ts
@@ -202,7 +202,15 @@ function renderHookHandlers(
   const wrapped = options.requireError
     ? `    if (input?.error) {\n${statements.map((line) => `      ${line}`).join("\n")}\n    }`
     : rendered
+
+  // Wrap tool.execute.before handlers in try-catch to prevent a failing hook
+  // from crashing parallel tool call batches (causes API 400 errors).
+  // See: https://github.com/EveryInc/compound-engineering-plugin/issues/85
+  const isPreToolUse = event === "tool.execute.before"
   const note = options.note ? `    // ${options.note}\n` : ""
+  if (isPreToolUse) {
+    return `    "${event}": async (input) => {\n${note}    try {\n  ${wrapped}\n    } catch (err) {\n      console.error("[hook] ${event} error (non-fatal):", err)\n    }\n    }`
+  }
   return `    "${event}": async (input) => {\n${note}${wrapped}\n    }`
 }
 
diff --git a/tests/converter.test.ts b/tests/converter.test.ts
index 873ce2b..dfac9ab 100644
--- a/tests/converter.test.ts
+++ b/tests/converter.test.ts
@@ -132,6 +132,18 @@ describe("convertClaudeToOpenCode", () => {
     expect(hookFile!.content).toContain("// timeout: 30s")
     expect(hookFile!.content).toContain("// Prompt hook for Write|Edit")
     expect(hookFile!.content).toContain("// Agent hook for Write|Edit: security-sentinel")
+
+    // PreToolUse (tool.execute.before) handlers are wrapped in try-catch
+    // to prevent hook failures from crashing parallel tool call batches (#85)
+    const beforeIdx = hookFile!.content.indexOf('"tool.execute.before"')
+    const afterIdx = hookFile!.content.indexOf('"tool.execute.after"')
+    const beforeBlock = hookFile!.content.slice(beforeIdx, afterIdx)
+    expect(beforeBlock).toContain("try {")
+    expect(beforeBlock).toContain("} catch (err) {")
+
+    // PostToolUse (tool.execute.after) handlers are NOT wrapped in try-catch
+    const afterBlock = hookFile!.content.slice(afterIdx, hookFile!.content.indexOf('"session.created"'))
+    expect(afterBlock).not.toContain("try {")
   })
 
   test("converts MCP servers", async () => {