diff --git a/repl.lua b/repl.lua
index b5f33f8..4041171 100644
--- a/repl.lua
+++ b/repl.lua
@@ -142,6 +142,22 @@ function M.run(config)
         if sess.version_warning then
             renderer.status("mcp " .. alias .. ": " .. sess.version_warning)
         end
+        -- Tool-name validation (issue #32): Anthropic via Bedrock enforces
+        -- ^[a-zA-Z0-9_-]{1,128}$. We use "__" as the alias separator, so the
+        -- emitted name is alias__tool. Warn at startup; emit anyway so local
+        -- llama.cpp users aren't penalized for lenient downstreams.
+        if alias:find("__", 1, true) then
+            renderer.status(("mcp %s: alias contains '__' (used as separator); "
+                .. "tool dispatch will misparse"):format(alias))
+        end
+        for _, t in ipairs(sess:list_tools()) do
+            local full = alias .. "__" .. (t.name or "")
+            if #full > 128 or full:find("[^%w_-]") then
+                renderer.status(("mcp %s: tool name '%s' violates "
+                    .. "^[a-zA-Z0-9_-]{1,128}$ (will fail with strict providers "
+                    .. "e.g. anthropic via Bedrock)"):format(alias, full))
+            end
+        end
         return true, #sess:list_tools()
     end