fix(puppeteer): return isError instead of internal error on navigation failure#4051
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…n failure puppeteer_navigate throws an unhandled Protocol error when given an invalid URL (e.g., empty string, malformed URL). The CDP error propagates as a JSON-RPC -32603 internal error, which prevents agents from detecting and recovering from the failure. Wrap page.goto() in a try/catch and return isError: true with the error message, matching the pattern used by puppeteer_screenshot and other tools in this server. Reproduction: mcp-assert audit --server "npx @modelcontextprotocol/server-puppeteer" # puppeteer_navigate: CRASH (internal error) Found with mcp-assert (https://github.com/blackwell-systems/mcp-assert)
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Apr 26, 2026
7 tools discovered, 7 assertions. 1 bug: puppeteer_navigate crashes with internal error on invalid URLs instead of returning isError. Fix PR submitted (modelcontextprotocol/servers#4051). Server #40.
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Summary
puppeteer_navigatethrows an unhandled CDPProtocol errorwhen given an invalid or empty URL. The error propagates as a JSON-RPC-32603internal error, which prevents agents from detecting and recovering from the failure.The fix wraps
page.goto()in a try/catch and returnsisError: truewith the error message, matching the pattern already used bypuppeteer_screenshot(which correctly catches missing selectors and returnsisError: true).Reproduction
Manual reproduction: call
puppeteer_navigatewith{"url": ""}or{"url": "not-a-url"}.Expected:
{ isError: true, content: [{ text: "Navigation failed: ..." }] }Actual: JSON-RPC
-32603internal error (unhandled exception)Change
One-line change in
src/puppeteer/index.ts: wrap the existingpage.goto(args.url)call in a try/catch block that returns a structuredisError: trueresponse on failure.Found with mcp-assert, a testing tool for MCP servers.