rohitg00/ai-engineering-from-scratch · error · ContractViolation

tools/list failed

Error message

tools/list failed

What it means

Error "tools/list failed" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at phases/13-tools-and-protocols/28-mcp-tool-contracts-and-content/code/main.py:699

        self.server = server
        self.principal = principal
        self.max_list_pages = max_list_pages
        self.rejections: list[dict[str, str]] = []
        self.cursor_trace: list[str | None] = []
        self.tools: dict[str, dict[str, Any]] = {}

    def discover_tools(self) -> dict[str, dict[str, Any]]:
        cursor: str | None = None
        request_id = 1
        seen_cursors: set[str] = set()
        for _ in range(self.max_list_pages):
            params: dict[str, Any] = {}
            if cursor is not None:
                params["cursor"] = cursor
            self.cursor_trace.append(cursor)
            response = self.server.dispatch(make_request(request_id, "tools/list", params))
            if response is None or "error" in response:
                raise ContractViolation("tools/list failed")
            result = response["result"]
            for tool in result["tools"]:
                try:
                    validate_tool_descriptor(tool)
                except ContractViolation as exc:
                    self.rejections.append({"tool": tool.get("name", "<unknown>"), "reason": str(exc)})
                    continue
                self.tools[tool["name"]] = tool
            next_cursor = result.get("nextCursor")
            if next_cursor is None:
                return self.tools
            if not isinstance(next_cursor, str):
                raise ContractViolation("tools/list nextCursor must be a string or null")
            if next_cursor in seen_cursors:
                raise ContractViolation("tools/list returned a repeated or cyclic nextCursor")
            seen_cursors.add(next_cursor)
            cursor = next_cursor
            request_id += 1

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at phases/13-tools-and-protocols/28-mcp-tool-contracts-and-content/code/main.py:699 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/7ec550c4898b811a. Report an issue: GitHub.