Show the UTC weekday in the Timestamp Converter

docs/tool-guide.md

@@ -58,8 +58,12 @@ other whitespace is significant. Empty input is supported.
 
 `value` is a string. `to_iso` accepts Unix **seconds**, including fractions and
 negative values. `to_unix` accepts an ISO 8601 date/time with `Z` or a UTC offset.
-Both return `unix_seconds` and `iso_utc`. For example,
-`convert_timestamp("1970-01-01T05:30:00+05:30", "to_unix")` returns zero seconds.
+Both return `unix_seconds`, `iso_utc`, and `weekday_utc`, the English weekday name
+of the converted UTC date. For example,
+`convert_timestamp("1970-01-01T05:30:00+05:30", "to_unix")` returns zero seconds,
+and `convert_timestamp("1970-01-02T00:30:00+01:00", "to_unix")` is Thursday in UTC
+even though the input's local date is Friday. A fixed Monday-to-Sunday list is used,
+so the name does not depend on the machine's locale.
 Timezone-less dates are rejected so results do not depend on the machine's timezone.
 Python datetime's year range (1–9999) and microsecond precision apply; finer fractional
 seconds may be rounded. Invalid, infinite, or out-of-range values raise `ValueError`.

src/mcp_tools_lab/tools/timestamps.py

@@ -4,11 +4,16 @@
 from datetime import datetime, timedelta, timezone
 from typing import Literal
 
+# A fixed list keeps the name in English whatever the machine's locale is.
+WEEKDAYS = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
+
 
 def convert_timestamp(value: str, direction: Literal["to_iso", "to_unix"] = "to_iso") -> dict:
     """Convert Unix seconds to UTC ISO 8601, or an offset-aware ISO date to seconds.
 
     ISO input must include a time and timezone, such as 2026-01-01T12:00:00+05:30.
+
+    weekday_utc is the English weekday name of the converted UTC date.
     """
     epoch = datetime(1970, 1, 1, tzinfo=timezone.utc)
     try:
@@ -27,4 +32,8 @@ def convert_timestamp(value: str, direction: Literal["to_iso", "to_unix"] = "to_
             raise ValueError("direction must be to_iso or to_unix.")
     except (ValueError, OverflowError) as error:
         raise ValueError(f"Cannot convert timestamp: {error}") from error
-    return {"unix_seconds": seconds, "iso_utc": date.isoformat().replace("+00:00", "Z")}
+    return {
+        "unix_seconds": seconds,
+        "iso_utc": date.isoformat().replace("+00:00", "Z"),
+        "weekday_utc": WEEKDAYS[date.weekday()],
+    }

tests/test_timestamps.py

@@ -18,3 +18,23 @@ def test_fractional_and_negative_seconds():
 def test_invalid_input(value, direction):
     with pytest.raises(ValueError, match="Cannot convert"):
         convert_timestamp(value, direction)
+
+
+def test_weekday_utc_for_known_days():
+    assert convert_timestamp("0")["weekday_utc"] == "Thursday"
+    assert convert_timestamp("345600")["weekday_utc"] == "Monday"
+    assert convert_timestamp("1970-01-04T00:00:00Z", "to_unix")["weekday_utc"] == "Sunday"
+
+
+def test_weekday_utc_uses_utc_not_the_inputs_local_date():
+    result = convert_timestamp("1970-01-02T00:30:00+01:00", "to_unix")
+    assert result["iso_utc"] == "1970-01-01T23:30:00Z"
+    assert result["weekday_utc"] == "Thursday"
+
+
+def test_weekday_utc_for_negative_timestamp():
+    assert convert_timestamp("-0.5")["weekday_utc"] == "Wednesday"
+
+
+def test_weekday_utc_in_both_directions():
+    assert convert_timestamp("0")["weekday_utc"] == convert_timestamp("1970-01-01T00:00:00Z", "to_unix")["weekday_utc"]