diff --git a/README.md b/README.md
index 2730c9aa..3a32537c 100644
--- a/README.md
+++ b/README.md
@@ -117,6 +117,8 @@ Start at the layer that matches your task:
   each product carries its own `README.md`, `ARCHITECTURE.md`, `docs/`,
   and `specs/`
 - [`tests/README.md`](tests/README.md) — host-test workflow
+- [`docs/local_http_api.md`](docs/local_http_api.md) — product-neutral local
+  HTTP API, mDNS discovery, and AirGradient Go support
 
 When adding or editing any Markdown file:
 
diff --git a/components/airgradient-local-server/README.md b/components/airgradient-local-server/README.md
index aacab4ca..b1cfe194 100644
--- a/components/airgradient-local-server/README.md
+++ b/components/airgradient-local-server/README.md
@@ -8,8 +8,8 @@ supply live data and config semantics through small abstract providers.
 ## Status
 
 `Stable`. The component and its host tests are implemented, and the Go source
-integration is documented in the
-[Go Local Server service doc](../../products/go/docs/local_server.md).
+integration is documented in the [Local HTTP API guide](../../docs/local_http_api.md)
+and the [Go Local Server service doc](../../products/go/docs/local_server.md).
 
 ## Scope
 
diff --git a/docs/local_http_api.md b/docs/local_http_api.md
new file mode 100644
index 00000000..c6cef85f
--- /dev/null
+++ b/docs/local_http_api.md
@@ -0,0 +1,333 @@
+# Local HTTP API
+
+AirGradient devices can expose a versioned HTTP API on a local network. The
+API lets local clients read the latest measurements, inspect active device
+configuration, submit supported configuration changes, and trigger supported
+actions. Product and operating-mode support varies; clients must discover a
+device's capabilities rather than assuming every endpoint, field, or action is
+available.
+
+## Availability and Discovery
+
+A device exposes the API only while its product and active operating mode allow
+local network access. When it does, it advertises the following mDNS service:
+
+| Property | Value |
+|---|---|
+| Service type | `_airgradient._tcp` |
+| Hostname | `airgradient_<serial>.local` |
+| API version TXT record | `api=1` |
+| Identity TXT records | `vendor=AirGradient`, `model`, `serialno`, `fw_ver` |
+
+`serialno` is the same value returned as `serialNumber` by the measures
+endpoint. Clients should use the service record's advertised host and port;
+they must not assume a fixed port. If mDNS is unavailable on the client
+network, use the device's LAN address instead.
+
+## Security
+
+The local API uses plain HTTP. It does not provide TLS, authentication,
+authorization, or a CORS policy. Use it only on a trusted, appropriately
+isolated LAN and never expose it directly to an untrusted or public network.
+
+## Quick Start
+
+Replace the hostname with the address discovered through mDNS or the device's
+LAN address.
+
+```sh
+export AG_URL="http://airgradient_ABCDEF123456.local"
+curl "$AG_URL/api/v1/measures"
+curl "$AG_URL/api/v1/config"
+```
+
+## Endpoints
+
+| Method | Path | Success | Purpose |
+|---|---|---:|---|
+| `GET` | `/api/v1/measures` | `200` | Read the latest valid measurements and device identity. |
+| `GET` | `/api/v1/config` | `200` | Read the active configuration supported by the product. |
+| `PUT` | `/api/v1/config` | `202` | Submit a partial configuration update. |
+| `POST` | `/api/v1/actions/calibrate-co2` | `200` | Request CO2 calibration when supported. |
+| `POST` | `/api/v1/actions/test-leds` | `200` | Request an LED diagnostic when supported. |
+
+An endpoint can be absent when the product does not expose that capability. In
+that case, the HTTP server returns its normal `404` response. A registered
+action that the current product does not support returns a structured `404`
+error instead.
+
+### Read Measurements
+
+`GET /api/v1/measures` returns a JSON object containing device identity and
+the latest valid readings. `serialNumber`, `model`, `firmware`, and `boot` are
+always present. `boot` is the completed uptime in minutes. `wifiRssi` is in
+dBm and is present only when link quality is available.
+
+All other measurement fields are optional. A product omits a field when it
+lacks the sensor or the latest value is invalid; it does not send JSON `null`.
+
+#### Identity and Link Fields
+
+| Field | JSON Type | Units / Values | Description |
+|---|---|---|---|
+| `serialNumber` | String | — | Device serial number. Always present. |
+| `model` | String | — | AirGradient product model identifier. Always present. |
+| `firmware` | String | — | Firmware version. Always present. |
+| `boot` | Integer | Completed minutes | Uptime for the current boot session, saturated at `4294967295`. Always present. |
+| `wifiRssi` | Integer | dBm | Received Wi-Fi signal strength. Omitted when unavailable. |
+
+#### Air Measurements
+
+| Field | JSON Type | Units / Values | Description |
+|---|---|---|---|
+| `co2` | Integer | ppm | Carbon dioxide concentration. |
+| `pm01` | Number | µg/m³ | PM1.0 mass concentration. |
+| `pm25` | Number | µg/m³ | PM2.5 mass concentration. |
+| `pm10` | Number | µg/m³ | PM10 mass concentration. |
+| `temperature` | Number | °C | Air temperature. This remains Celsius regardless of a display-unit setting. |
+| `humidity` | Number | %RH | Relative humidity. |
+| `tvocIndex` | Integer | Index | TVOC gas index. |
+| `tvocRaw` | Integer | Sensor raw value | TVOC sensor raw reading. |
+| `noxIndex` | Integer | Index | NOx gas index. |
+| `noxRaw` | Integer | Sensor raw value | NOx sensor raw reading. |
+
+PM mass is rounded to one decimal place. Temperature and humidity are rounded
+to two decimal places.
+
+#### Particle Count Fields
+
+| Field | JSON Type | Units / Values | Description |
+|---|---|---|---|
+| `pm003Count` | Integer | Particle count | Particles with a 0.3 µm size threshold. |
+| `pm005Count` | Integer | Particle count | Particles with a 0.5 µm size threshold. |
+| `pm01Count` | Integer | Particle count | Particles with a 1.0 µm size threshold. |
+| `pm02Count` | Integer | Particle count | Particles with a 2.5 µm size threshold. |
+| `pm50Count` | Integer | Particle count | Particles with a 5.0 µm size threshold. |
+| `pm10Count` | Integer | Particle count | Particles with a 10 µm size threshold. |
+
+Particle counts are rounded to whole numbers. The sensor determines the count
+sample volume; clients must not infer a concentration unit from these fields.
+
+#### Power Fields
+
+| Field | JSON Type | Units / Values | Description |
+|---|---|---|---|
+| `battPercent` | Integer | % | Battery charge percentage. |
+| `battVolt` | Number | V | Battery voltage. |
+| `chargeVolt` | Number | V | Charging-input voltage; it is not a charging-state indicator. |
+
+Voltages are rounded to two decimal places.
+
+```json
+{
+  "serialNumber": "ABCDEF123456",
+  "model": "P-1PSG",
+  "firmware": "1.2.3",
+  "boot": 42,
+  "wifiRssi": -58,
+  "co2": 612,
+  "pm25": 4.3,
+  "temperature": 21.75,
+  "humidity": 47.2
+}
+```
+
+### Read Configuration
+
+`GET /api/v1/config` returns the complete active subset supported by the
+device. Products omit unsupported fields. A client should use this response as
+the capability source for subsequent configuration writes.
+
+The configuration catalog below defines all standardized v1 fields. The generic
+parser enforces each JSON type and the listed enum values. Products define the
+supported subset and enforce product-specific ranges, URLs, country formats,
+and cross-field policy.
+
+#### Device and Display Fields
+
+| Field | JSON Type | Values | Description |
+|---|---|---|---|
+| `country` | String | Product-defined | Country or region identifier. |
+| `pmStandard` | String | `ugm3`, `us-aqi` | PM display standard: mass concentration or US AQI. |
+| `temperatureUnit` | String | `c`, `f` | Display temperature unit. Measurements remain Celsius. |
+| `measurementInterval` | Integer | Seconds; product-defined range | Measurement interval. |
+| `gpsMode` | String | `off`, `tracking`, `always` | GPS operating mode. |
+| `frontLedBrightness` | Integer | Product-defined range | Front LED brightness. |
+| `backLedBrightness` | Integer | Product-defined range | Back or AQI LED brightness. |
+| `touchLedIntensity` | Integer | Product-defined range | Touch LED intensity. |
+| `buzzerEnabled` | Boolean | `true`, `false` | Buzzer enablement. |
+| `ledMode` | String | `co2`, `pm`, `iaqs`, `off` | LED display mode. |
+| `ledBarBrightness` | Integer | Product-defined range | LED bar brightness. |
+| `displayBrightness` | Integer | Product-defined range | Display brightness. |
+
+#### Connectivity and Sensor Fields
+
+| Field | JSON Type | Values | Description |
+|---|---|---|---|
+| `postDataToCloud` | Boolean | `true`, `false` | Cloud measurement-posting enablement. |
+| `cloudConnection` | Boolean | `true`, `false` | Cloud connection enablement. |
+| `configurationControl` | String | `cloud`, `local`, `both` | Permitted remote configuration sources. |
+| `co2AbcDays` | Integer | Days; product-defined range | CO2 automatic background-calibration period. |
+| `tvocLearningOffset` | Integer | Hours; product-defined range | TVOC gas-index learning offset. |
+| `noxLearningOffset` | Integer | Hours; product-defined range | NOx gas-index learning offset. |
+| `mqttBrokerUrl` | String | Product-defined URL | MQTT broker URL. |
+| `httpDomain` | String | Product-defined host or URL | HTTP service domain. |
+| `corrections` | Object | [Correction Object](#correction-object) | PM2.5, temperature, and humidity corrections. |
+
+#### Correction Object
+
+`corrections` contains zero or more of `pm25`, `temperature`, and `humidity`.
+Each is a correction entry. The table describes the entry shape used in both
+GET responses and PUT requests.
+
+| Field | JSON Type | Applies To | Description |
+|---|---|---|---|
+| `correctionAlgorithm` | String | All entries | Product-supported correction algorithm. |
+| `slr` | Object or `null` | All entries | Simple linear regression parameters, or `null` when none apply. |
+| `slr.intercept` | Number | All non-null SLRs | SLR intercept. |
+| `slr.scalingFactor` | Number | All non-null SLRs | SLR scaling factor. |
+| `slr.useEpa2021` | Boolean | `pm25` only | Whether the PM2.5 correction uses the EPA 2021 adjustment. |
+
+Clients should send both `intercept` and `scalingFactor` for a non-null `slr`.
+Products validate accepted algorithms, coefficients, and partial-update
+semantics. `useEpa2021` is not valid for temperature or humidity corrections.
+
+### Write Configuration
+
+`PUT /api/v1/config` accepts a JSON object containing only the fields to
+change. The body must be complete, valid JSON, and use only recognized fields.
+For example, a client may request a supported PM display standard:
+
+```sh
+curl -X PUT "$AG_URL/api/v1/config" \
+  -H "Content-Type: application/json" \
+  --data '{"pmStandard":"us-aqi"}'
+```
+
+`202 Accepted` has an empty body. It confirms that the device accepted the
+validated update for later processing; it does not confirm persistence or
+runtime application. Poll `GET /api/v1/config` until the requested values are
+visible, using a client-selected deadline. An empty object is a valid no-op
+when writes are allowed.
+
+### Trigger Actions
+
+Actions are fire-and-forget requests with an empty `200` response. A successful
+response confirms only that the device accepted the request; it does not report
+start, progress, or completion. For example:
+
+```sh
+curl -X POST "$AG_URL/api/v1/actions/calibrate-co2"
+```
+
+The v1 action catalog contains these actions:
+
+| Action | Endpoint | Request Body | Description |
+|---|---|---|---|
+| CO2 calibration | `POST /api/v1/actions/calibrate-co2` | None | Request CO2 calibration. |
+| LED test | `POST /api/v1/actions/test-leds` | None | Request the device LED diagnostic. |
+
+An action may be unavailable for a product, current device state, or device
+policy. Unsupported actions return `404 not_found`; rejected actions return
+`403 forbidden`; and temporarily unavailable actions return `503 busy`.
+
+## Errors
+
+Local API errors use an `application/json` response body. `field` is present
+when a specific configuration field caused the error.
+
+```json
+{
+  "error": {
+    "code": "invalid_value",
+    "field": "pmStandard",
+    "message": "invalid value"
+  }
+}
+```
+
+| Status | Code | Client Action |
+|---:|---|---|
+| `400` | `invalid_body` | Correct the JSON request body. |
+| `400` | `unknown_field` | Remove the unknown field or use a supported API version. |
+| `400` | `invalid_value` | Correct the value or its type. |
+| `403` | `forbidden` | The current policy or state does not allow the operation. |
+| `404` | `not_found` | The requested known field or action is unsupported by this product. |
+| `503` | `busy` | Retry later with client-controlled backoff. |
+| `500` | `internal` | Treat as a device-side failure and retry only when appropriate. |
+
+`503` responses do not include a `Retry-After` header. Paths outside the local
+API route catalog use the HTTP server's normal `404` response rather than this
+error envelope.
+
+## Compatibility and Capabilities
+
+The API version is in the path: `/api/v1/`. Within a version, clients must
+preserve unknown response fields and tolerate omitted optional fields. A product
+may support a subset of the shared measurement, configuration, and action
+catalog. Read configuration before writing it, and handle `404 not_found` for
+model-specific fields and actions.
+
+## AirGradient Go Support
+
+AirGradient Go exposes the local API in Stationary mode after Wi-Fi obtains an
+IP address. It uses the common mDNS discovery contract above. The API remains
+available by LAN address through a transient reconnect after it has first been
+activated; its mDNS advertisement follows Wi-Fi address availability.
+
+### Supported Endpoints
+
+| Method | Path | Availability | Purpose |
+|---|---|---|---|
+| `GET` | `/api/v1/measures` | Always while the Go local API is active | Read the latest corrected measurements and device identity. |
+| `GET` | `/api/v1/config` | Always while the Go local API is active | Read Go's active local-API configuration. |
+| `PUT` | `/api/v1/config` | When local configuration writes are allowed | Submit supported Go configuration changes. |
+| `POST` | `/api/v1/actions/calibrate-co2` | When actions are allowed | Request CO2 calibration. |
+| `POST` | `/api/v1/actions/test-leds` | When actions are allowed | Request the LED diagnostic. |
+
+### Measures Fields
+
+Go returns the following fields from `GET /api/v1/measures`. Identity fields
+are always present. All other fields are present only when their latest value is
+valid; `wifiRssi` is present only while Stationary Wi-Fi is online.
+
+| Field Group | Fields |
+|---|---|
+| Identity | `serialNumber`, `model`, `firmware`, `boot` |
+| Link | `wifiRssi` |
+| Air measurements | `co2`, `pm01`, `pm25`, `pm10`, `temperature`, `humidity`, `tvocIndex`, `tvocRaw`, `noxIndex`, `noxRaw` |
+| Particle counts | `pm003Count`, `pm005Count`, `pm01Count`, `pm02Count`, `pm50Count`, `pm10Count` |
+| Power | `battPercent`, `battVolt`, `chargeVolt` |
+
+Local measurement values use Go's corrected PM2.5, temperature, and humidity
+values.
+
+### Configuration Fields
+
+Go returns these fields from `GET /api/v1/config` and accepts them in partial
+`PUT /api/v1/config` requests when its local-write policy allows the request.
+
+| Field Group | Supported Fields |
+|---|---|
+| Device behavior | `pmStandard`, `temperatureUnit`, `measurementInterval`, `gpsMode` |
+| LEDs and buzzer | `frontLedBrightness`, `backLedBrightness`, `touchLedIntensity`, `buzzerEnabled` |
+| Connectivity policy | `cloudConnection`, `configurationControl` |
+| Sensor configuration | `co2AbcDays`, `tvocLearningOffset`, `noxLearningOffset`, `corrections` |
+
+### Actions
+
+| Action | Endpoint | Availability |
+|---|---|---|
+| CO2 calibration | `POST /api/v1/actions/calibrate-co2` | Available when actions are allowed. |
+| LED test | `POST /api/v1/actions/test-leds` | Available when actions are allowed. |
+
+`configurationControl` determines whether local configuration writes, cloud
+configuration Fetch, or both are permitted. `cloudConnection` controls cloud
+communication but does not disable the local API or mDNS. During a committed
+Stationary Wi-Fi OTA, Go keeps its available local endpoint read-only: GET
+requests continue to return cached snapshots, while valid writes and actions
+return `403 forbidden`.
+
+See the [Go Local Server service doc](../products/go/docs/local_server.md) for
+the complete Go lifecycle, configuration ranges, and asynchronous request
+handling details.
diff --git a/products/go/README.md b/products/go/README.md
index b4a4cbe6..a22f35eb 100644
--- a/products/go/README.md
+++ b/products/go/README.md
@@ -161,8 +161,10 @@ partition table, and merged factory-flash binary.
 - [`docs/`](docs) — per-service implementation notes (BLE, cloud, display,
   GPS, input, Local Server, orchestrator, OTA, power, sensor producer,
   settings, storage, UI, Wi-Fi)
-- [`docs/local_server.md`](docs/local_server.md) — Stationary local HTTP API,
-  mDNS discovery, request queue, and OTA access policy
+- [`../../docs/local_http_api.md`](../../docs/local_http_api.md) — local HTTP
+  API, mDNS discovery, and AirGradient Go support
+- [`docs/local_server.md`](docs/local_server.md) — Local Server lifecycle,
+  request queue, and OTA access policy
 - [`docs/measurement_corrections.md`](docs/measurement_corrections.md) — raw
   and corrected measurement views and their consumers
 - [`docs/fg_learning.md`](docs/fg_learning.md) — factory fuel-gauge learning