diff --git a/server/app.py b/server/app.py
index ae50578..60b1353 100644
--- a/server/app.py
+++ b/server/app.py
@@ -13,6 +13,7 @@ import logging
 import os
 import re
 import uuid
+from datetime import datetime, timedelta, timezone
 from typing import Any, Optional
 from urllib.parse import urlparse
 
@@ -22,7 +23,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse, RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel, ConfigDict, Field
-from sqlalchemy import select, delete, func
+from sqlalchemy import select, delete, func, or_
 from sqlalchemy.orm import Session
 from starlette.middleware.sessions import SessionMiddleware
 
@@ -3413,6 +3414,101 @@ def usage_ping(body: UsageIn, user: models.User = Depends(auth.get_current_user)
     return {"ok": True}
 
 
+def _parse_date_q(v: str, end: bool = False) -> Optional[datetime]:
+    """Accepts a plain YYYY-MM-DD (what a <input type=date> sends) or a full
+    ISO datetime. A date-only `to` means "through the end of that day", not
+    midnight at its start - otherwise a range of "today" would match nothing
+    from today at all."""
+    if not v:
+        return None
+    try:
+        d = datetime.fromisoformat(v)
+    except ValueError:
+        return None
+    if d.tzinfo is None:
+        d = d.replace(tzinfo=timezone.utc)
+    if end and len(v) <= 10:  # date-only
+        d = d + timedelta(days=1) - timedelta(microseconds=1)
+    return d
+
+
+def _usage_query(db: Session, caller: "models.User", date_from, date_to, project_id, username, tool):
+    """Shared by the summary and export endpoints so the two can never
+    disagree about which rows a filter set matches - the export is a raw
+    dump of exactly what the summary counted, not a separately-derived view."""
+    stmt = select(models.UsageEvent)
+    managed = managed_project_ids(db, caller)
+    if managed is not None:
+        # A project_super_user (never an app admin, who gets managed=None) is
+        # scoped to events tied to a project they administer, plus their OWN
+        # suite-wide activity (admin console opens etc. carry no project_id) -
+        # never another user's activity outside what they manage.
+        if managed:
+            stmt = stmt.where(or_(
+                models.UsageEvent.project_id.in_(managed),
+                models.UsageEvent.username == caller.username,
+            ))
+        else:
+            stmt = stmt.where(models.UsageEvent.username == caller.username)
+    df = _parse_date_q(date_from)
+    dt = _parse_date_q(date_to, end=True)
+    if df:
+        stmt = stmt.where(models.UsageEvent.at >= df)
+    if dt:
+        stmt = stmt.where(models.UsageEvent.at <= dt)
+    if project_id:
+        stmt = stmt.where(models.UsageEvent.project_id == project_id)
+    if username:
+        stmt = stmt.where(models.UsageEvent.username == username)
+    if tool:
+        stmt = stmt.where(models.UsageEvent.tool == tool)
+    return stmt.order_by(models.UsageEvent.at)
+
+
+@app.get("/api/usage/summary")
+def usage_summary(
+    date_from: Optional[str] = Query(None, alias="from"),
+    date_to: Optional[str] = Query(None, alias="to"),
+    project_id: Optional[str] = Query(None),
+    username: Optional[str] = Query(None),
+    tool: Optional[str] = Query(None),
+    caller: models.User = Depends(require_user_manager),
+    db: Session = Depends(get_db),
+):
+    """CR-019. Same gate as the User Directory (require_user_manager): an app
+    admin or a project_super_user with at least one managed project. Filters
+    combine. Aggregated in Python over the filtered row set rather than a SQL
+    GROUP BY - correct and simple at today's scale; if usage_events grows
+    into the millions (plausible, given retention is indefinite by decision),
+    the day/week/month bucketing here is the first thing to move server-side
+    into SQL. Not done now because nothing currently requires it."""
+    rows = db.scalars(_usage_query(db, caller, date_from, date_to, project_id, username, tool)).all()
+
+    by_day: dict[str, set] = {}
+    by_week: dict[str, set] = {}
+    by_month: dict[str, set] = {}
+    per_user_last: dict[str, datetime] = {}
+    per_tool: dict[str, int] = {}
+    for e in rows:
+        by_day.setdefault(e.at.date().isoformat(), set()).add(e.username)
+        by_week.setdefault(e.at.strftime("%G-W%V"), set()).add(e.username)
+        by_month.setdefault(e.at.strftime("%Y-%m"), set()).add(e.username)
+        if e.username not in per_user_last or e.at > per_user_last[e.username]:
+            per_user_last[e.username] = e.at
+        per_tool[e.tool] = per_tool.get(e.tool, 0) + 1
+
+    return {
+        "active_users": {
+            "by_day": {k: len(v) for k, v in sorted(by_day.items())},
+            "by_week": {k: len(v) for k, v in sorted(by_week.items())},
+            "by_month": {k: len(v) for k, v in sorted(by_month.items())},
+        },
+        "per_user_last_active": {u: models._iso(t) for u, t in sorted(per_user_last.items())},
+        "by_tool": dict(sorted(per_tool.items(), key=lambda kv: -kv[1])),
+        "event_count": len(rows),
+    }
+
+
 @app.get("/api/comments")
 def list_comments(
     source: Optional[str] = Query(None),