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

recognized parameter header is duplicated

Error message

recognized parameter header is duplicated

What it means

Error "recognized parameter header is duplicated" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at phases/13-tools-and-protocols/28-mcp-tool-contracts-and-content/code/main.py:625

    for supplied_name, supplied_value in headers.items():
        normalized.setdefault(supplied_name.casefold(), []).append(
            (supplied_name, supplied_value)
        )

    checked_names: list[str] = []
    properties = tool["inputSchema"].get("properties", {})
    for path, suffix in validate_header_annotations(tool):
        expected_name = f"Mcp-Param-{suffix}"
        supplied = normalized.get(expected_name.casefold(), [])
        body_value = _read_path(arguments, path)
        if body_value is MISSING:
            if supplied:
                raise ContractViolation("recognized parameter header has no body argument")
            continue
        if not supplied:
            raise ContractViolation("recognized parameter header is missing")
        if len(supplied) != 1:
            raise ContractViolation("recognized parameter header is duplicated")
        decoded = decode_parameter_header_value(supplied[0][1])
        expected = _parameter_text(body_value, properties[path[0]]["type"])
        if decoded != expected:
            raise ContractViolation("recognized parameter header does not match the body")
        checked_names.append(expected_name)

    audit_log.append(
        {
            "event": "parameter_headers_validated",
            "headerNames": sorted(checked_names),
        }
    )


def streamable_http_tool_call(
    server: ContractServer,
    request: dict[str, Any],
    headers: dict[str, str],

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:625 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/65f8d0f7d8241306. Report an issue: GitHub.