diff --git a/PLAN.md b/PLAN.md
index ebafed8..ecce4af 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -176,6 +176,18 @@ something long in one, switch away and back, refresh — it's all still there.
   the daemon's sampling clock; the chart window is always 300 samples, so 30 s at 100 ms
   and 10 min at 2 s. Still to do: persistent
   history (SQLite ring, e.g. 10 s × 7 days), SMART (`smartctl -j`), longer time ranges.
+- **Sensors** — **step 1 shipped 2026-09-19** (`internal/sensors`,
+  `internal/metrics/sensors.go`, reference in `SENSORS.md`): everything measured is a
+  sensor with a stable dotted ID; catalog, single value (`?format=text`), per-sensor
+  history, and a **shaped query** where the client sends the object it wants and gets it
+  back filled in (GraphQL's idea without GraphQL: sensors differ per machine, so a static
+  schema would collapse to `sensor(id:)` anyway). `/api/metrics` and the Dashboard are
+  untouched so far. **Remaining, in order:** (2) read-only scoped tokens + Prometheus
+  `/metrics`; (3) push stream + widget library, Dashboard rebuilt on its own sensors;
+  (4) embeddable widget page + Glance config (Glance's `custom-api` only refetches on page
+  load, an `iframe` of our embed is what's live); (5) non-metric sensors — services,
+  SMART, ZFS, updates, containers. One sampler rate, set in one place, is part of (3):
+  today the open dashboard still drives it.
 - **Multi-host** — **Phase 1 shipped 2026-09-18** (`internal/nodes`, `internal/tlsauto`,
   `MachineSwitcher.tsx`, `Machines.tsx`). One binary, hub and spoke: a host whose
   `config.json` lists `nodes` is a hub; any other is a standalone node with its full UI.
diff --git a/SENSORS.md b/SENSORS.md
new file mode 100644
index 0000000..d7782c9
--- /dev/null
+++ b/SENSORS.md
@@ -0,0 +1,84 @@
+# Sensors — the standard read interface
+
+Everything Ham Lab measures is a **sensor**: a stable dotted ID, a little metadata, a
+current value. Any consumer — Ham Lab's own dashboard, Glance, Home Assistant, a shell
+script — discovers them from the catalog and asks for exactly the ones it wants.
+
+Code: `internal/sensors` (types, registry, selectors, shaped query) and
+`internal/metrics/sensors.go` (the collector as a provider). The registry measures
+nothing; providers do. A new source of sensors implements `sensors.Provider` and is
+added to the registry in `api.New`.
+
+## IDs
+
+```
+cpu.usage  cpu.core.<n>.usage  cpu.temp  load.1|5|15  uptime
+mem.total|used|avail|free|cached|buffers|used_pct     swap.total|used|avail|used_pct
+temp.<chip>.<label>            fan.<chip>.<label>
+net.<iface>.rx|tx|rx_total|tx_total|up
+disk.<dev>.read|write|util|size|temp
+fs.<mount>.size|used|used_pct
+ups.battery|runtime|load|load_pct|in_v|out_v|on_battery|state|source
+```
+
+- Segments are lower case `[a-z0-9_-]`: `Package id 0` → `package_id_0`, `/mnt/tank` →
+  `mnt_tank`, `/` → `root`. The real names are in the sensor's `labels`.
+- Built from names the hardware reports, never enumeration order (`hwmon3` moves between
+  boots). Two identical chips collide; the second gets `_2`.
+- Which sensors exist differs per machine. That is the point of the catalog.
+
+## A sensor
+
+```json
+{ "id": "temp.coretemp.package_id_0", "name": "coretemp Package id 0",
+  "kind": "temperature", "unit": "°C", "value": 51, "t": 1789826600878,
+  "warn": 105, "crit": 105, "labels": { "chip": "coretemp", "label": "Package id 0" } }
+```
+
+`value` is a number, bool or string. `t` is when it was really read, in unix ms — slow
+sections (filesystems 30 s, UPS 10 s) are older than the tick. `min`/`max` are the scale
+(0–100 for percentages, 0–total for used bytes); `warn`/`crit` are the hardware's own
+thresholds where it states them.
+
+## Endpoints
+
+All behind the same auth as the rest of `/api` (session cookie or `Authorization: Bearer`).
+On a hub, every one is also at `/api/nodes/<machine>/sensors…` for each managed machine.
+
+| | |
+|---|---|
+| `GET /api/sensors` | Catalog, with current values. `?ids=fan.*,cpu.usage` narrows it. |
+| `GET /api/sensors/{id}` | One sensor. `?format=text` → the bare value as text/plain. |
+| `GET /api/sensors/{id}/history` | `{id, unit, t[], v[]}` — what the ring holds (300 samples at the sampling interval). Numbers only. |
+| `POST /api/sensors/query` | Shaped query, below. |
+| `GET /api/sensors/query?k=selector&…` | The same, flat, for consumers that can only fetch a URL. |
+
+A selector is an exact ID or a glob. `*` crosses dots: `fan.*` is every fan,
+`cpu.core.*.usage` every core.
+
+## Shaped query
+
+Send the object you want, with selectors where the values go. Get it back filled in.
+
+```
+POST /api/sensors/query
+{ "cpu": "cpu.usage", "fans": "fan.*", "box": { "temp": "cpu.temp", "up": "uptime" } }
+
+→ { "cpu": 12.4,
+    "fans": { "fan.nct6775.fan1": 820, "fan.nct6775.fan2": 1140 },
+    "box": { "temp": 41, "up": 80520 } }
+```
+
+- Exact ID → its value; `null` if this machine has no such sensor (so one query works
+  across machines that differ).
+- Glob → an object keyed by ID; `{}` if nothing matches.
+- Objects and arrays are walked; anything else in a query is a 400.
+- `?full=1` → every value is the whole sensor object instead of the bare value. (In the
+  GET form `full` is therefore not usable as a key.)
+
+## Not yet
+
+Read-only scoped tokens, Prometheus `/metrics`, a push stream, widgets built on this,
+an embeddable widget page, and non-metric sensors (services, SMART, ZFS, updates). Until
+scoped tokens exist, **do not hand a Ham Lab token to a dashboard** — today's tokens are
+full control of the machine.
diff --git a/internal/api/server.go b/internal/api/server.go
index 535fd42..7e0e80d 100644
--- a/internal/api/server.go
+++ b/internal/api/server.go
@@ -34,6 +34,7 @@ import (
 	"hamlab/internal/metrics"
 	"hamlab/internal/nodes"
 	"hamlab/internal/priv"
+	"hamlab/internal/sensors"
 	"hamlab/internal/services"
 	"hamlab/internal/setup"
 	"hamlab/internal/storage"
@@ -54,6 +55,7 @@ type Server struct {
 	limiter     auth.Limiter
 	mgr         *term.Manager
 	metrics     *metrics.Collector
+	sensors     *sensors.Registry
 	store       *store.Store
 	svc         *services.Manager
 	cron        *cron.Manager
@@ -74,7 +76,7 @@ type Server struct {
 
 func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *metrics.Collector, st *store.Store, svc *services.Manager, cr *cron.Manager, tm *tasks.Manager, up *updates.Manager, sto *storage.Manager, fsLocal, fsSudo files.FS, nm *nodes.Manager, fingerprint string, ui fs.FS, version string) *Server {
 	host, _ := os.Hostname()
-	s := &Server{cfg: cfg, sessions: sessions, mgr: mgr, metrics: col, store: st, svc: svc, cron: cr, tasks: tm, updates: up, storage: sto, fsLocal: fsLocal, fsSudo: fsSudo, nodes: nm, fingerprint: fingerprint, ui: ui, version: version,
+	s := &Server{cfg: cfg, sessions: sessions, mgr: mgr, metrics: col, sensors: sensors.NewRegistry(col), store: st, svc: svc, cron: cr, tasks: tm, updates: up, storage: sto, fsLocal: fsLocal, fsSudo: fsSudo, nodes: nm, fingerprint: fingerprint, ui: ui, version: version,
 		started: time.Now(), host: host, user: os.Getenv("USER")}
 	if u, err := user.Current(); err == nil && u.Username != "" {
 		s.user = u.Username
@@ -109,6 +111,11 @@ func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *me
 	m.HandleFunc("GET /api/terminals/{id}/attach", s.auth(s.attach))
 	m.HandleFunc("GET /api/metrics", s.auth(s.metricsLatest))
 	m.HandleFunc("GET /api/metrics/history", s.auth(s.metricsHistory))
+	m.HandleFunc("GET /api/sensors", s.auth(s.sensorCatalog))
+	m.HandleFunc("GET /api/sensors/query", s.auth(s.sensorQuery))
+	m.HandleFunc("POST /api/sensors/query", s.auth(s.sensorQuery))
+	m.HandleFunc("GET /api/sensors/{id}", s.auth(s.sensorOne))
+	m.HandleFunc("GET /api/sensors/{id}/history", s.auth(s.sensorHistory))
 	m.HandleFunc("GET /api/services", s.auth(s.listServices))
 	m.HandleFunc("GET /api/services/{unit}", s.auth(s.showService))
 	m.HandleFunc("GET /api/services/{unit}/file", s.auth(s.serviceFile))
@@ -568,6 +575,82 @@ func (s *Server) metricsHistory(w http.ResponseWriter, _ *http.Request) {
 	jsonOK(w, 200, s.metrics.History())
 }
 
+// ---- sensors: the standard read interface (SENSORS.md) ----
+
+// sensorCatalog lists every sensor with its current value; ?ids= narrows it with
+// comma-separated IDs or globs.
+func (s *Server) sensorCatalog(w http.ResponseWriter, r *http.Request) {
+	all := s.sensors.All()
+	if ids := r.URL.Query().Get("ids"); ids != "" {
+		picked := []sensors.Sensor{}
+		for _, sel := range strings.Split(ids, ",") {
+			got, err := sensors.Select(all, strings.TrimSpace(sel))
+			if err != nil {
+				jsonErr(w, 400, err.Error())
+				return
+			}
+			picked = append(picked, got...)
+		}
+		all = picked
+	}
+	jsonOK(w, 200, map[string]any{"sensors": all})
+}
+
+// sensorOne is a single sensor; ?format=text is the bare value, for shell scripts and
+// anything else that can only fetch a URL and read a number.
+func (s *Server) sensorOne(w http.ResponseWriter, r *http.Request) {
+	got, _ := sensors.Select(s.sensors.All(), r.PathValue("id"))
+	if len(got) != 1 {
+		jsonErr(w, 404, "no such sensor")
+		return
+	}
+	if r.URL.Query().Get("format") == "text" {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		fmt.Fprintln(w, got[0].Value)
+		return
+	}
+	jsonOK(w, 200, got[0])
+}
+
+func (s *Server) sensorHistory(w http.ResponseWriter, r *http.Request) {
+	h, ok := s.sensors.History(r.PathValue("id"))
+	if !ok {
+		jsonErr(w, 404, "no history for that sensor")
+		return
+	}
+	jsonOK(w, 200, h)
+}
+
+// sensorQuery answers a shaped query. POST sends the shape as the body; GET builds a
+// flat one from the query string (?cpu=cpu.usage&fans=fan.*). ?full=1 returns whole
+// sensors instead of bare values.
+func (s *Server) sensorQuery(w http.ResponseWriter, r *http.Request) {
+	full := r.URL.Query().Get("full") == "1"
+	var q json.RawMessage
+	if r.Method == http.MethodPost {
+		b, err := io.ReadAll(http.MaxBytesReader(w, r.Body, 64<<10))
+		if err != nil {
+			jsonErr(w, 413, "query larger than 64 KiB")
+			return
+		}
+		q = b
+	} else {
+		flat := map[string]string{}
+		for k, v := range r.URL.Query() {
+			if k != "full" && len(v) > 0 {
+				flat[k] = v[0]
+			}
+		}
+		q, _ = json.Marshal(flat)
+	}
+	out, err := sensors.Shape(s.sensors.All(), q, full)
+	if err != nil {
+		jsonErr(w, 400, err.Error())
+		return
+	}
+	jsonOK(w, 200, out)
+}
+
 // ---- services (systemd) ----
 
 func (s *Server) listServices(w http.ResponseWriter, r *http.Request) {
diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index bbc8909..7f3ab7c 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -132,6 +132,8 @@ type Sample struct {
 	FS       []FS       `json:"fs"`
 	UPS      *UPS       `json:"ups"`
 	Uptime   float64    `json:"uptime"`
+
+	fsT, upsT int64 // when the slow sections were really read; sensors report these, not T
 }
 
 // Series is the compact history the UI seeds its sparklines from.
@@ -292,11 +294,11 @@ func (c *Collector) sample() {
 	if c.lastFS == nil || now.Sub(c.fsAt) >= fsEvery {
 		c.lastFS, c.fsAt = filesystems(), now
 	}
-	s.FS = c.lastFS
+	s.FS, s.fsT = c.lastFS, c.fsAt.UnixMilli()
 	if c.upsProbe != nil && (c.upsAt.IsZero() || now.Sub(c.upsAt) >= upsEvery) {
 		c.lastUPS, c.upsAt = c.upsProbe(), now
 	}
-	s.UPS = c.lastUPS
+	s.UPS, s.upsT = c.lastUPS, c.upsAt.UnixMilli()
 
 	if first {
 		return // deltas are meaningless on the priming pass
diff --git a/internal/metrics/sensors.go b/internal/metrics/sensors.go
new file mode 100644
index 0000000..803322e
--- /dev/null
+++ b/internal/metrics/sensors.go
@@ -0,0 +1,169 @@
+package metrics
+
+import (
+	"fmt"
+	"strconv"
+
+	"hamlab/internal/sensors"
+)
+
+// The collector as a sensors.Provider: every number in a Sample, one sensor each. The
+// IDs are built from names the hardware reports (chip, label, interface, device, mount),
+// never from enumeration order like hwmon3, which moves between boots.
+
+// flattener turns one Sample into sensors. With only set it builds just that one, so
+// walking the whole ring for a history costs string compares, not allocations.
+type flattener struct {
+	only string
+	seen map[string]int
+	out  []sensors.Sensor
+}
+
+type bounds struct{ min, max, warn, crit *float64 }
+
+var pct = bounds{min: sensors.F(0), max: sensors.F(100)}
+
+func upTo(max float64) bounds { return bounds{min: sensors.F(0), max: sensors.F(max)} }
+
+func (f *flattener) add(id, name, kind, unit string, v any, t int64, b bounds, labels ...string) {
+	f.seen[id]++
+	if n := f.seen[id]; n > 1 { // two identical chips: the second is coretemp_2
+		id = fmt.Sprintf("%s_%d", id, n)
+	}
+	if f.only != "" && id != f.only {
+		return
+	}
+	s := sensors.Sensor{ID: id, Name: name, Kind: kind, Unit: unit, Value: v, T: t, Min: b.min, Max: b.max, Warn: b.warn, Crit: b.crit}
+	if len(labels) > 0 {
+		s.Labels = make(map[string]string, len(labels)/2)
+		for i := 0; i+1 < len(labels); i += 2 {
+			s.Labels[labels[i]] = labels[i+1]
+		}
+	}
+	f.out = append(f.out, s)
+}
+
+func ratio(part, whole uint64) float64 {
+	if whole == 0 {
+		return 0
+	}
+	return round1(float64(part) / float64(whole) * 100)
+}
+
+func flatten(s Sample, only string) []sensors.Sensor {
+	f := &flattener{only: only, seen: map[string]int{}}
+	t, none := s.T, bounds{}
+
+	f.add("cpu.usage", "CPU", "usage", "%", s.CPU, t, pct)
+	for i, c := range s.Cores {
+		n := strconv.Itoa(i)
+		f.add("cpu.core."+n+".usage", "Core "+n, "usage", "%", c, t, pct, "core", n)
+	}
+	if c := cpuTemp(s.Temps); c > 0 {
+		f.add("cpu.temp", "CPU temperature", "temperature", "°C", c, t, none)
+	}
+	for i, w := range []string{"1", "5", "15"} {
+		f.add("load."+w, "Load "+w+" min", "load", "", s.Load[i], t, none)
+	}
+	f.add("uptime", "Uptime", "duration", "s", s.Uptime, t, none)
+
+	for _, m := range []struct {
+		id, name string
+		v        Mem
+	}{{"mem", "Memory", s.Mem}, {"swap", "Swap", s.Swap}} {
+		f.add(m.id+".total", m.name+" total", "bytes", "B", float64(m.v.Total), t, none)
+		f.add(m.id+".used", m.name+" used", "bytes", "B", float64(m.v.Used), t, upTo(float64(m.v.Total)))
+		f.add(m.id+".avail", m.name+" available", "bytes", "B", float64(m.v.Avail), t, upTo(float64(m.v.Total)))
+		f.add(m.id+".used_pct", m.name+" used", "usage", "%", ratio(m.v.Used, m.v.Total), t, pct)
+	}
+	f.add("mem.free", "Memory free", "bytes", "B", float64(s.Mem.Free), t, upTo(float64(s.Mem.Total)))
+	f.add("mem.cached", "Memory cached", "bytes", "B", float64(s.Mem.Cached), t, upTo(float64(s.Mem.Total)))
+	f.add("mem.buffers", "Memory buffers", "bytes", "B", float64(s.Mem.Buffers), t, upTo(float64(s.Mem.Total)))
+
+	for _, x := range s.Temps {
+		b := bounds{}
+		if x.Max > 0 {
+			b.warn = sensors.F(x.Max)
+		}
+		if x.Crit > 0 {
+			b.crit = sensors.F(x.Crit)
+		}
+		f.add(sensors.ID("temp", sensors.Seg(x.Chip), sensors.Seg(x.Label)), x.Chip+" "+x.Label, "temperature", "°C", x.C, t, b, "chip", x.Chip, "label", x.Label)
+	}
+	for _, x := range s.Fans {
+		f.add(sensors.ID("fan", sensors.Seg(x.Chip), sensors.Seg(x.Label)), x.Chip+" "+x.Label, "fan", "rpm", float64(x.RPM), t, none, "chip", x.Chip, "label", x.Label)
+	}
+
+	for _, x := range s.Net {
+		p := "net." + sensors.Seg(x.Iface)
+		f.add(p+".rx", x.Iface+" receive", "rate", "B/s", x.RxBps, t, none, "iface", x.Iface)
+		f.add(p+".tx", x.Iface+" transmit", "rate", "B/s", x.TxBps, t, none, "iface", x.Iface)
+		f.add(p+".rx_total", x.Iface+" received", "bytes", "B", float64(x.RxTotal), t, none, "iface", x.Iface)
+		f.add(p+".tx_total", x.Iface+" transmitted", "bytes", "B", float64(x.TxTotal), t, none, "iface", x.Iface)
+		f.add(p+".up", x.Iface+" link", "state", "", x.Up, t, none, "iface", x.Iface)
+	}
+
+	for _, x := range s.Disks {
+		p := "disk." + sensors.Seg(x.Name)
+		f.add(p+".read", x.Name+" read", "rate", "B/s", x.ReadBps, t, none, "device", x.Name, "model", x.Model)
+		f.add(p+".write", x.Name+" write", "rate", "B/s", x.WriteBps, t, none, "device", x.Name, "model", x.Model)
+		f.add(p+".util", x.Name+" busy", "usage", "%", x.UtilPct, t, pct, "device", x.Name, "model", x.Model)
+		f.add(p+".size", x.Name+" size", "bytes", "B", float64(x.Size), t, none, "device", x.Name, "model", x.Model)
+		if x.Temp > 0 {
+			f.add(p+".temp", x.Name+" temperature", "temperature", "°C", x.Temp, t, none, "device", x.Name, "model", x.Model)
+		}
+	}
+
+	for _, x := range s.FS {
+		p := "fs." + sensors.Seg(x.Mount)
+		f.add(p+".size", x.Mount+" size", "bytes", "B", float64(x.Size), s.fsT, none, "mount", x.Mount, "fstype", x.Type)
+		f.add(p+".used", x.Mount+" used", "bytes", "B", float64(x.Used), s.fsT, upTo(float64(x.Size)), "mount", x.Mount, "fstype", x.Type)
+		f.add(p+".used_pct", x.Mount+" used", "usage", "%", ratio(x.Used, x.Size), s.fsT, pct, "mount", x.Mount, "fstype", x.Type)
+	}
+
+	if u := s.UPS; u != nil {
+		ut := s.upsT
+		f.add("ups.battery", "UPS battery", "usage", "%", u.BatteryPct, ut, pct, "model", u.Model)
+		f.add("ups.runtime", "UPS runtime", "duration", "min", u.RuntimeMin, ut, none, "model", u.Model)
+		f.add("ups.load", "UPS load", "power", "W", u.LoadW, ut, none, "model", u.Model)
+		f.add("ups.load_pct", "UPS load", "usage", "%", u.LoadPct, ut, pct, "model", u.Model)
+		f.add("ups.in_v", "UPS input", "voltage", "V", u.InV, ut, none, "model", u.Model)
+		f.add("ups.out_v", "UPS output", "voltage", "V", u.OutV, ut, none, "model", u.Model)
+		f.add("ups.on_battery", "UPS on battery", "state", "", u.OnBattery, ut, none, "model", u.Model)
+		f.add("ups.state", "UPS state", "state", "", u.State, ut, none, "model", u.Model)
+		f.add("ups.source", "UPS power source", "state", "", u.Source, ut, none, "model", u.Model)
+	}
+	return f.out
+}
+
+// Sensors implements sensors.Provider.
+func (c *Collector) Sensors() []sensors.Sensor {
+	s, ok := c.Latest()
+	if !ok {
+		return nil
+	}
+	return flatten(s, "")
+}
+
+// SensorHistory implements sensors.Historian: the ring, seen through one sensor. Samples
+// where the sensor didn't exist (a disk plugged in since) are left out, not zero-filled.
+func (c *Collector) SensorHistory(id string) (sensors.Series, bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	out := sensors.Series{ID: id, T: []int64{}, V: []float64{}}
+	found := false
+	for _, smp := range c.ring {
+		got := flatten(smp, id)
+		if len(got) == 0 {
+			continue
+		}
+		found = true
+		v, ok := got[0].Value.(float64)
+		if !ok {
+			return sensors.Series{}, false // states have no curve
+		}
+		out.Unit = got[0].Unit
+		out.T, out.V = append(out.T, smp.T), append(out.V, v)
+	}
+	return out, found
+}
diff --git a/internal/metrics/sensors_test.go b/internal/metrics/sensors_test.go
new file mode 100644
index 0000000..48fc68c
--- /dev/null
+++ b/internal/metrics/sensors_test.go
@@ -0,0 +1,50 @@
+package metrics
+
+import "testing"
+
+func TestFlatten(t *testing.T) {
+	s := Sample{T: 1000, CPU: 10, Cores: []float64{5, 15}, Mem: Mem{Total: 200, Used: 50},
+		Temps: []Temp{{Chip: "nvme", Label: "Composite", C: 40, Crit: 85}, {Chip: "nvme", Label: "Composite", C: 45}},
+		Fans:  []Fan{{Chip: "nct6775", Label: "fan2", RPM: 1100}},
+		FS:    []FS{{Mount: "/", Size: 100, Used: 25}}, fsT: 900}
+	got := map[string]any{}
+	for _, x := range flatten(s, "") {
+		if _, dup := got[x.ID]; dup {
+			t.Errorf("duplicate id %s", x.ID)
+		}
+		got[x.ID] = x.Value
+	}
+	for id, want := range map[string]any{"cpu.usage": 10.0, "cpu.core.1.usage": 15.0, "mem.used_pct": 25.0, "temp.nvme.composite": 40.0,
+		"temp.nvme.composite_2": 45.0, "fan.nct6775.fan2": 1100.0, "fs.root.used_pct": 25.0} {
+		if got[id] != want {
+			t.Errorf("%s = %v, want %v", id, got[id], want)
+		}
+	}
+	one := flatten(s, "temp.nvme.composite_2")
+	if len(one) != 1 || one[0].Value != 45.0 {
+		t.Errorf("only: got %+v", one)
+	}
+	for _, x := range flatten(s, "fs.root.used") {
+		if x.T != 900 {
+			t.Errorf("fs sensor should carry the fs read time, got %d", x.T)
+		}
+	}
+}
+
+func TestSensorHistory(t *testing.T) {
+	c := NewCollector()
+	c.ring = []Sample{{T: 1, CPU: 10}, {T: 2, CPU: 20, Net: []Net{{Iface: "eth0", Up: true, RxBps: 5}}}}
+	h, ok := c.SensorHistory("cpu.usage")
+	if !ok || len(h.V) != 2 || h.V[1] != 20 || h.Unit != "%" {
+		t.Fatalf("cpu: %+v %v", h, ok)
+	}
+	if h, ok := c.SensorHistory("net.eth0.rx"); !ok || len(h.V) != 1 || h.T[0] != 2 {
+		t.Fatalf("net: a sensor that appeared later has a shorter history, got %+v %v", h, ok)
+	}
+	if _, ok := c.SensorHistory("net.eth0.up"); ok {
+		t.Error("a state has no history")
+	}
+	if _, ok := c.SensorHistory("nope"); ok {
+		t.Error("unknown id")
+	}
+}
diff --git a/internal/sensors/sensors.go b/internal/sensors/sensors.go
new file mode 100644
index 0000000..58ee838
--- /dev/null
+++ b/internal/sensors/sensors.go
@@ -0,0 +1,217 @@
+// Package sensors is the one standard way anything reads what Ham Lab measures.
+//
+// Every measurable thing is a Sensor: a stable dotted ID ("cpu.core.3.usage",
+// "fan.nct6775.fan2", "fs.root.used_pct"), a little metadata, and a current value. A
+// consumer discovers them from the catalog, then asks for exactly the ones it wants —
+// one by ID, many by glob, or as a shaped query where the client sends the object it
+// wants and gets it back with the values filled in. See SENSORS.md.
+//
+// Sources of sensors are Providers. The registry only joins them; it measures nothing.
+package sensors
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"path"
+	"sort"
+	"strings"
+)
+
+// Sensor is one measurable thing and its reading. Value is a float64, bool or string.
+type Sensor struct {
+	ID     string            `json:"id"`
+	Name   string            `json:"name"`           // human label
+	Kind   string            `json:"kind"`           // usage | load | temperature | fan | rate | bytes | duration | voltage | power | state
+	Unit   string            `json:"unit,omitempty"` // % · °C · rpm · B/s · B · s · min · V · W · MHz
+	Value  any               `json:"value"`
+	T      int64             `json:"t"` // unix ms the value was read — slow sensors are older than the tick
+	Min    *float64          `json:"min,omitempty"`
+	Max    *float64          `json:"max,omitempty"`
+	Warn   *float64          `json:"warn,omitempty"` // the hardware's own thresholds, where it states them
+	Crit   *float64          `json:"crit,omitempty"`
+	Labels map[string]string `json:"labels,omitempty"` // the real names behind the ID: chip, iface, mount…
+}
+
+// Series is a numeric sensor's recent past.
+type Series struct {
+	ID   string    `json:"id"`
+	Unit string    `json:"unit,omitempty"`
+	T    []int64   `json:"t"`
+	V    []float64 `json:"v"`
+}
+
+// Provider is a source of sensors. Sensors returns every sensor it has, with current values.
+type Provider interface {
+	Sensors() []Sensor
+}
+
+// Historian is a Provider that also remembers. ok is false for an ID it doesn't hold.
+type Historian interface {
+	SensorHistory(id string) (s Series, ok bool)
+}
+
+// F is a pointer to a float, for the optional bounds.
+func F(v float64) *float64 { return &v }
+
+// Seg makes one ID segment from a real-world name: lower case, [a-z0-9_-] only, so IDs
+// survive URLs, query strings and templating languages untouched. "Package id 0" →
+// "package_id_0", "/mnt/tank" → "mnt_tank", "/" → "root".
+func Seg(name string) string {
+	if name == "/" {
+		return "root"
+	}
+	var b strings.Builder
+	gap := false
+	for _, r := range strings.ToLower(strings.TrimSpace(name)) {
+		switch {
+		case r >= 'a' && r <= 'z', r >= '0' && r <= '9', r == '-':
+			if gap && b.Len() > 0 {
+				b.WriteByte('_')
+			}
+			gap = false
+			b.WriteRune(r)
+		default:
+			gap = true
+		}
+	}
+	if b.Len() == 0 {
+		return "unnamed"
+	}
+	return b.String()
+}
+
+// ID joins already-safe segments.
+func ID(segs ...string) string { return strings.Join(segs, ".") }
+
+// Registry joins providers into one namespace.
+type Registry struct{ providers []Provider }
+
+func NewRegistry(p ...Provider) *Registry { return &Registry{providers: p} }
+
+func (r *Registry) Add(p Provider) { r.providers = append(r.providers, p) }
+
+// All returns every sensor, sorted by ID. Two sensors that would share an ID (two
+// identical chips) get "_2", "_3" on the colliding one, in the provider's order.
+func (r *Registry) All() []Sensor {
+	var out []Sensor
+	seen := map[string]int{}
+	for _, p := range r.providers {
+		for _, s := range p.Sensors() {
+			seen[s.ID]++
+			if n := seen[s.ID]; n > 1 {
+				s.ID = fmt.Sprintf("%s_%d", s.ID, n)
+			}
+			out = append(out, s)
+		}
+	}
+	sort.SliceStable(out, func(i, j int) bool { return out[i].ID < out[j].ID })
+	return out
+}
+
+// History finds the provider that remembers id.
+func (r *Registry) History(id string) (Series, bool) {
+	for _, p := range r.providers {
+		if h, ok := p.(Historian); ok {
+			if s, ok := h.SensorHistory(id); ok {
+				return s, true
+			}
+		}
+	}
+	return Series{}, false
+}
+
+// IsGlob reports whether a selector names many sensors rather than one.
+func IsGlob(sel string) bool { return strings.ContainsAny(sel, "*?[") }
+
+// Select returns the sensors a selector names: an exact ID, or a glob where * crosses
+// dots ("fan.*" is every fan, "cpu.core.*.usage" every core).
+func Select(all []Sensor, sel string) ([]Sensor, error) {
+	if !IsGlob(sel) {
+		for _, s := range all {
+			if s.ID == sel {
+				return []Sensor{s}, nil
+			}
+		}
+		return nil, nil
+	}
+	if _, err := path.Match(sel, ""); err != nil {
+		return nil, fmt.Errorf("bad pattern %q", sel)
+	}
+	var out []Sensor
+	for _, s := range all {
+		if ok, _ := path.Match(sel, s.ID); ok {
+			out = append(out, s)
+		}
+	}
+	return out, nil
+}
+
+// Shape answers a shaped query: the client sends the object it wants, with selectors
+// where the values go, and gets the same object back with them filled in.
+//
+//	{"cpu": "cpu.usage", "fans": "fan.*", "box": {"up": "uptime"}}
+//	→ {"cpu": 12.4, "fans": {"fan.nct6775.fan1": 820}, "box": {"up": 80520}}
+//
+// An exact ID becomes its value (null if there is no such sensor here — machines differ,
+// and a dashboard shouldn't fail because one has no fans). A glob becomes an object keyed
+// by ID. Objects and arrays are walked. With full, every value is the whole Sensor.
+func Shape(all []Sensor, query json.RawMessage, full bool) (any, error) {
+	var q any
+	if err := json.Unmarshal(query, &q); err != nil {
+		return nil, errors.New("query is not valid JSON")
+	}
+	return shape(all, q, full, 0)
+}
+
+func shape(all []Sensor, q any, full bool, depth int) (any, error) {
+	if depth > 16 {
+		return nil, errors.New("query nested too deep")
+	}
+	leaf := func(s Sensor) any {
+		if full {
+			return s
+		}
+		return s.Value
+	}
+	switch v := q.(type) {
+	case string:
+		got, err := Select(all, v)
+		if err != nil {
+			return nil, err
+		}
+		if !IsGlob(v) {
+			if len(got) == 0 {
+				return nil, nil
+			}
+			return leaf(got[0]), nil
+		}
+		m := make(map[string]any, len(got))
+		for _, s := range got {
+			m[s.ID] = leaf(s)
+		}
+		return m, nil
+	case map[string]any:
+		m := make(map[string]any, len(v))
+		for k, sub := range v {
+			r, err := shape(all, sub, full, depth+1)
+			if err != nil {
+				return nil, err
+			}
+			m[k] = r
+		}
+		return m, nil
+	case []any:
+		a := make([]any, len(v))
+		for i, sub := range v {
+			r, err := shape(all, sub, full, depth+1)
+			if err != nil {
+				return nil, err
+			}
+			a[i] = r
+		}
+		return a, nil
+	default:
+		return nil, fmt.Errorf("a query holds sensor IDs, objects and arrays; got %v", v)
+	}
+}
diff --git a/internal/sensors/sensors_test.go b/internal/sensors/sensors_test.go
new file mode 100644
index 0000000..ca4e3e5
--- /dev/null
+++ b/internal/sensors/sensors_test.go
@@ -0,0 +1,53 @@
+package sensors
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+)
+
+type fake []Sensor
+
+func (f fake) Sensors() []Sensor { return f }
+
+func TestSeg(t *testing.T) {
+	for in, want := range map[string]string{"/": "root", "/mnt/tank": "mnt_tank", "Package id 0": "package_id_0", "enp3s0": "enp3s0", "  ": "unnamed", "Tctl+": "tctl", "nvme0n1": "nvme0n1"} {
+		if got := Seg(in); got != want {
+			t.Errorf("Seg(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+func TestRegistryDedupes(t *testing.T) {
+	r := NewRegistry(fake{{ID: "temp.nvme.composite", Value: 40.0}}, fake{{ID: "temp.nvme.composite", Value: 50.0}})
+	all := r.All()
+	if len(all) != 2 || all[0].ID != "temp.nvme.composite" || all[1].ID != "temp.nvme.composite_2" {
+		t.Fatalf("got %+v", all)
+	}
+}
+
+func TestShape(t *testing.T) {
+	all := []Sensor{{ID: "cpu.usage", Value: 12.5, Unit: "%"}, {ID: "fan.a.fan1", Value: 800.0}, {ID: "fan.a.fan2", Value: 900.0}, {ID: "net.eth0.up", Value: true}}
+	got, err := Shape(all, json.RawMessage(`{"cpu":"cpu.usage","fans":"fan.*","box":{"link":"net.eth0.up","gone":"ups.battery"},"list":["cpu.usage"]}`), false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]any{
+		"cpu":  12.5,
+		"fans": map[string]any{"fan.a.fan1": 800.0, "fan.a.fan2": 900.0},
+		"box":  map[string]any{"link": true, "gone": nil},
+		"list": []any{12.5},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %#v\nwant %#v", got, want)
+	}
+	full, _ := Shape(all, json.RawMessage(`"cpu.usage"`), true)
+	if s, ok := full.(Sensor); !ok || s.Unit != "%" {
+		t.Fatalf("full: got %#v", full)
+	}
+	for _, bad := range []string{`{"x": 5}`, `{"x": "fan.["}`, `not json`} {
+		if _, err := Shape(all, json.RawMessage(bad), false); err == nil {
+			t.Errorf("Shape(%s) should fail", bad)
+		}
+	}
+}