diff --git a/.mcp.json b/.mcp.json
new file mode 100644
index 0000000..340b0f4
--- /dev/null
+++ b/.mcp.json
@@ -0,0 +1,10 @@
+{
+  "mcpServers": {
+    "screen-locker": {
+      "type": "stdio",
+      "command": "${HOME}/.venvs/screen-locker-mcp/bin/python",
+      "args": ["-m", "screen_locker._mcp"],
+      "env": {}
+    }
+  }
+}
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..80c5e22
--- /dev/null
+++ b/README.md
@@ -0,0 +1,32 @@
+# screen-locker
+
+Tkinter/systemd screen locker with workout tracking, sick-day management, and
+wake-alarm integration. It enforces a workout cadence by locking the screen
+until a RunnerUp-verified (or explicitly justified) workout is logged.
+
+## MCP server (Claude Code integration)
+
+screen-locker exposes a **read-only** MCP server (`screen_locker._mcp`) so
+Claude Code and its subagents can query workout compliance and the
+lock-decision state through typed tools — without shelling out to the
+`screen-locker-status` CLI or opening the Tk window.
+
+- **Read-only tools:** `get_status` (full status snapshot), `get_summary`
+  (one-line i3blocks summary + `ok`/`warn`/`lock` state word), `explain_lock`
+  (why the screen is / isn't locked right now), `get_flags` (the individual
+  boolean lock-decision predicates for today).
+- There are **no write/action tools**, by design. Nothing here logs a workout
+  or mutates state — workouts are logged only from RunnerUp-verified TCX data,
+  never from a caller's claim. No tool exposes the sync token or any HMAC key.
+
+The `mcp` SDK is an optional dependency (`pip install -e '.[mcp]'`), kept out of
+the CLI/systemd system-python path. One-time setup of the dedicated venv that
+Claude Code spawns:
+
+```bash
+./scripts/setup_mcp.sh
+```
+
+Registration lives in the checked-in [`.mcp.json`](./.mcp.json) (project scope).
+Restart Claude Code in this repo and approve the project MCP-server prompt for it
+to load. Verify with `claude mcp list`.
diff --git a/pyproject.toml b/pyproject.toml
index 12b7221..c8e257f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -11,6 +11,14 @@ dependencies = [
 [project.scripts]
 screen-locker-status = "screen_locker.status_view:main"
 
+# Optional extras. The `mcp` group is ONLY needed by the read-only MCP server
+# (screen_locker._mcp), which Claude Code spawns via a dedicated venv (see
+# scripts/setup_mcp.sh / .mcp.json). It is deliberately NOT a core dependency
+# so the systemd/CLI system-python path stays dependency-light and never has
+# to import the MCP SDK.
+[project.optional-dependencies]
+mcp = ["mcp>=1.9"]
+
 [tool.setuptools.packages.find]
 # This repo also holds stronglift_replacement/ (an unrelated Flutter app, not
 # a Python package); without this, setuptools' automatic flat-layout
diff --git a/screen_locker/_mcp.py b/screen_locker/_mcp.py
new file mode 100644
index 0000000..402c521
--- /dev/null
+++ b/screen_locker/_mcp.py
@@ -0,0 +1,141 @@
+"""Read-only MCP (Model Context Protocol) server for screen-locker.
+
+Exposes the locker's *read-only* status surface as typed MCP tools, so an MCP
+client (Claude Code and its subagents) can query today's/this week's workout
+compliance, the shutdown projection, and the lock-decision trace without
+shelling out to the ``screen-locker-status`` CLI or opening the Tk window.
+
+Run via the dedicated venv that has the ``mcp`` extra installed::
+
+    ~/.venvs/screen-locker-mcp/bin/python -m screen_locker._mcp
+
+(see ``scripts/setup_mcp.sh`` and the repo-root ``.mcp.json``).
+
+Safety invariants (do not break when adding tools):
+  * **READ-ONLY.** There are no write/action tools here, by design. In
+    particular there is deliberately **no** ``log_workout`` and no tool that
+    mutates workout/compliance state — the project rule is that workouts are
+    logged only from RunnerUp-verified TCX data, never from a caller's claim.
+    Every tool below calls only side-effect-free leaf helpers that *read*
+    on-disk state (``gather_status`` and the ``_compliance_state`` predicates),
+    never a mutating CLI/daemon entry point.
+  * **stdout is the JSON-RPC channel.** This module and every function a tool
+    calls must never write to stdout. All logging is routed to STDERR below,
+    and no tool calls ``screen_lock.py`` / ``status_view.main`` (which
+    ``print`` / open Tk windows / ``sys.exit``).
+  * **No secret ever leaves.** No tool returns the sync token
+    (``~/.config/screen_locker/sync_token``) or any HMAC key; the predicates
+    load only status/state and return booleans, and the status snapshot
+    carries no secret material.
+"""
+
+from __future__ import annotations
+
+from dataclasses import asdict
+import logging
+from pathlib import Path
+import sys
+from typing import Any
+
+from mcp.server.fastmcp import FastMCP
+
+from screen_locker._compliance_state import (
+    has_logged_today,
+    is_early_bird_pending,
+    is_scheduled_skip_today,
+    is_sick_day_today,
+)
+from screen_locker._constants import (
+    EARLY_BIRD_PENDING_FILE,
+    SCHEDULED_SKIPS_FILE,
+)
+from screen_locker._sick_tracker import load_history
+from screen_locker._status_data import format_summary_line, gather_status
+from screen_locker.status_view import _compliance_state_word
+
+# Log to STDERR only — STDOUT carries the MCP JSON-RPC protocol frames, so a
+# single stray stdout write would corrupt the stream and kill the session.
+logging.basicConfig(
+    level=logging.INFO,
+    stream=sys.stderr,
+    format="%(asctime)s [%(levelname)s] screen-locker-mcp: %(message)s",
+)
+logger = logging.getLogger(__name__)
+
+mcp = FastMCP("screen-locker")
+
+# The workout log lives beside the package, same default as
+# ``_status_data._DEFAULT_LOG_FILE``; declared here to avoid importing a
+# private name across modules.
+_LOG_FILE = Path(__file__).resolve().parent / "workout_log.json"
+
+
+# ──────────────────────────────────────────────────────────────
+# Read tools (state-only; never expose secrets, never mutate)
+# ──────────────────────────────────────────────────────────────
+
+
+@mcp.tool()
+def get_status() -> dict[str, Any]:
+    """Return the full read-only status snapshot.
+
+    A JSON-friendly projection of ``gather_status()``: today's and this week's
+    workout outcomes, the shutdown-time projection, the lock-decision trace,
+    and the rolling sick-day / manual-workout budgets. Reads on-disk state
+    only (no ADB, sudo, or network) and never mutates anything.
+    """
+    return asdict(gather_status())
+
+
+@mcp.tool()
+def get_summary() -> dict[str, Any]:
+    """Return the one-line i3blocks summary plus the compliance-state word.
+
+    ``summary_line`` is the same string the status bar shows
+    (``format_summary_line``); ``compliance_state`` is one of ``ok`` / ``warn``
+    / ``lock`` (``_compliance_state_word``).
+    """
+    snapshot = gather_status()
+    return {
+        "summary_line": format_summary_line(snapshot),
+        "compliance_state": _compliance_state_word(snapshot),
+    }
+
+
+@mcp.tool()
+def explain_lock() -> dict[str, Any]:
+    """Return why the screen is or is not being locked right now.
+
+    A JSON-friendly projection of the ``LockExplanation`` reconstruction of the
+    lock-decision chain (which skip condition fired, the full ordered trace,
+    and any pending auto-upgrade opportunity). Read-only: the heat-skip stage
+    is reported as not-evaluated rather than triggering a live ``wttr.in`` call.
+    """
+    return asdict(gather_status().lock_explanation)
+
+
+@mcp.tool()
+def get_flags() -> dict[str, bool]:
+    """Return the individual boolean lock-decision predicates for today.
+
+    Each predicate reads its own on-disk state file and degrades to ``False``
+    when that file is missing or unreadable — none of them mutate state or
+    expose secrets.
+    """
+    history = load_history()
+    return {
+        "has_logged_today": has_logged_today(_LOG_FILE),
+        "is_scheduled_skip_today": is_scheduled_skip_today(SCHEDULED_SKIPS_FILE),
+        "is_early_bird_pending": is_early_bird_pending(EARLY_BIRD_PENDING_FILE),
+        "is_sick_day_today": is_sick_day_today(history),
+    }
+
+
+def main() -> None:
+    """Run the MCP server over stdio (STDOUT = JSON-RPC, STDERR = logs)."""
+    logger.info("Starting screen-locker MCP server (python=%s)", sys.executable)
+    mcp.run()  # pragma: no cover
+
+
+if __name__ == "__main__":
+    main()
diff --git a/screen_locker/tests/test_mcp.py b/screen_locker/tests/test_mcp.py
new file mode 100644
index 0000000..46c8084
--- /dev/null
+++ b/screen_locker/tests/test_mcp.py
@@ -0,0 +1,147 @@
+"""Tests for the read-only MCP server tools in ``_mcp``.
+
+Helpers are patched at the ``_mcp`` module namespace (where they are imported),
+keeping each tool's own logic under test while isolating the already-tested
+leaf functions. ``get_status`` / ``explain_lock`` are exercised against a real
+:class:`StatusSnapshot` so the ``dataclasses.asdict`` conversion (and its
+JSON-friendliness) is covered for real, not mocked away.
+"""
+
+from __future__ import annotations
+
+from dataclasses import asdict
+import json
+from unittest.mock import patch
+
+from screen_locker import _mcp
+from screen_locker._compliance_state import (
+    AutoUpgradeOpportunity,
+    LockExplanation,
+    PredicateResult,
+)
+from screen_locker._status_data import (
+    DayStatus,
+    ManualWorkoutBudgetStatus,
+    ShutdownProjection,
+    ShutdownProjectionDay,
+    SickBudgetStatus,
+    StatusSnapshot,
+    WeeklySummary,
+)
+
+
+def _lock_explanation() -> LockExplanation:
+    return LockExplanation(
+        fired=True,
+        stage="full_lock_pending_heat_check",
+        reason="No skip condition applies.",
+        trace=(PredicateResult("scheduled_skip", fired=False, reason="not a skip"),),
+        auto_upgrade=AutoUpgradeOpportunity(
+            would_attempt=False, via="none", reason="No pending opportunity."
+        ),
+        heat_skip_evaluated=False,
+    )
+
+
+def _snapshot() -> StatusSnapshot:
+    day = DayStatus(
+        date="2026-07-10",
+        label="Fri Jul 10",
+        entry_type=None,
+        source="",
+        counted=False,
+        is_sick_day=False,
+    )
+    return StatusSnapshot(
+        today=day,
+        week=WeeklySummary(
+            days=(day,), counted_count=2, minimum=4, remaining=2, extra=0
+        ),
+        bonus_hours_this_week=0,
+        streak=1,
+        early_bird_extended=False,
+        shutdown=ShutdownProjection(
+            tonight=(22, 22, 5),
+            rest_of_week=(
+                ShutdownProjectionDay(label="Mon", hour=21, speculative=False),
+            ),
+            next_week_preview=(
+                ShutdownProjectionDay(label="Mon", hour=21, speculative=True),
+            ),
+            explanation="explanation text",
+        ),
+        lock_explanation=_lock_explanation(),
+        sick_budget=SickBudgetStatus(
+            used_7d=0,
+            budget_7d=1,
+            used_30d=0,
+            budget_30d=3,
+            used_90d=0,
+            budget_90d=10,
+            debt=0,
+            exhausted=False,
+        ),
+        manual_workout_budget=ManualWorkoutBudgetStatus(
+            used_7d=0, budget_7d=2, used_30d=0, budget_30d=5, exhausted=False
+        ),
+        generated_at="2026-07-10T12:00:00+00:00",
+    )
+
+
+class TestReadTools:
+    def test_get_status_returns_json_friendly_asdict(self) -> None:
+        snap = _snapshot()
+        with patch.object(_mcp, "gather_status", return_value=snap) as gs:
+            out = _mcp.get_status()
+        gs.assert_called_once_with()
+        assert out == asdict(snap)
+        # asdict output must be pure JSON (no datetime/dataclass leaks).
+        json.dumps(out)
+
+    def test_get_summary_combines_line_and_state(self) -> None:
+        with (
+            patch.object(_mcp, "gather_status") as gs,
+            patch.object(_mcp, "format_summary_line", return_value="LINE") as fsl,
+            patch.object(_mcp, "_compliance_state_word", return_value="ok") as csw,
+        ):
+            out = _mcp.get_summary()
+        assert out == {"summary_line": "LINE", "compliance_state": "ok"}
+        fsl.assert_called_once_with(gs.return_value)
+        csw.assert_called_once_with(gs.return_value)
+
+    def test_explain_lock_returns_lock_explanation_asdict(self) -> None:
+        snap = _snapshot()
+        with patch.object(_mcp, "gather_status", return_value=snap):
+            out = _mcp.explain_lock()
+        assert out == asdict(snap.lock_explanation)
+        assert out["fired"] is True
+        json.dumps(out)
+
+
+class TestGetFlags:
+    def test_flags_dict_and_predicate_wiring(self) -> None:
+        with (
+            patch.object(_mcp, "load_history", return_value="HIST") as lh,
+            patch.object(_mcp, "has_logged_today", return_value=True) as hlt,
+            patch.object(_mcp, "is_scheduled_skip_today", return_value=False) as iss,
+            patch.object(_mcp, "is_early_bird_pending", return_value=True) as iep,
+            patch.object(_mcp, "is_sick_day_today", return_value=False) as isd,
+        ):
+            out = _mcp.get_flags()
+        assert out == {
+            "has_logged_today": True,
+            "is_scheduled_skip_today": False,
+            "is_early_bird_pending": True,
+            "is_sick_day_today": False,
+        }
+        lh.assert_called_once_with()
+        hlt.assert_called_once_with(_mcp._LOG_FILE)
+        iss.assert_called_once_with(_mcp.SCHEDULED_SKIPS_FILE)
+        iep.assert_called_once_with(_mcp.EARLY_BIRD_PENDING_FILE)
+        isd.assert_called_once_with("HIST")
+
+
+def test_main_runs_stdio_server() -> None:
+    with patch.object(_mcp.mcp, "run") as run:
+        _mcp.main()
+    run.assert_called_once_with()
diff --git a/scripts/setup_mcp.sh b/scripts/setup_mcp.sh
new file mode 100755
index 0000000..6241517
--- /dev/null
+++ b/scripts/setup_mcp.sh
@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# ============================================================================
+# Set up the dedicated virtualenv that hosts the screen-locker MCP server.
+# Claude Code spawns this interpreter (see the repo-root .mcp.json) to run
+# `python -m screen_locker._mcp` over stdio.
+#
+# The MCP SDK (`mcp`) lives ONLY in this venv — it is an optional dependency,
+# deliberately kept out of the system/CLI/systemd python path. Both `mcp` and
+# `screen_locker` must be importable by this one interpreter or the MCP server
+# fails to start silently.
+#
+# The server is READ-ONLY: it exposes status/query tools only, never any tool
+# that logs a workout or mutates state.
+#
+# Idempotent: safe to re-run to pick up dependency changes.
+# ============================================================================
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+readonly SCRIPT_DIR REPO_DIR
+readonly VENV_DIR="${HOME}/.venvs/screen-locker-mcp"
+
+main() {
+    echo "== Setting up MCP venv at ${VENV_DIR} =="
+
+    if [[ ! -d "${VENV_DIR}" ]]; then
+        python3 -m venv "${VENV_DIR}"
+    fi
+
+    "${VENV_DIR}/bin/pip" install --quiet --upgrade pip
+    "${VENV_DIR}/bin/pip" install --quiet -e "${REPO_DIR}[mcp]"
+
+    echo "== Verifying imports =="
+    "${VENV_DIR}/bin/python" -c \
+        "import mcp, screen_locker; print('mcp + screen_locker import OK')"
+
+    echo
+    echo "Done. The server is registered via ${REPO_DIR}/.mcp.json"
+    echo "Restart Claude Code in this repo and approve the project MCP server prompt."
+}
+
+main "$@"