diff --git a/README.md b/README.md
index e6aeef3..1b7f062 100644
--- a/README.md
+++ b/README.md
@@ -9,32 +9,7 @@ The [NATS.io](https://nats.io/) based writing endpoint consumes messages in [thi
 
 ### REST API Endpoints
 
-In case `jwt-public-key` is a non-empty string in the `config.json` file, the API is protected by JWT based authentication. The signing algorithm has to be `Ed25519`, but no
-fields are required in the JWT payload. Expiration will be checked if specified. The JWT has to be provided using the HTTP `Authorization` header.
-
-All but one endpoints use *selectors* to access the data. A selector must be an array of strings or another array of strings. Examples are provided below.
-
-In the requests, `to` and `from` have to be UNIX timestamps in seconds. The response might also contain `from`/`to` timestamps. They can differ from those in the request,
-if there was not data for a section of the requested data.
-
-1. `POST /api/<from>/<to>/timeseries`
-    - Request-Body: `{ "selectors": [<sel1>, <sel2>, <sel3>, ...], "metrics": ["flops_any", "load_one", ...] }`
-    - The response will be a JSON array, each entry in the array corresponding to the selector found at that index in the request's `selectors` array
-    - Each array entry will be a map from every requested metric to this: `{ "from": Timestamp, "to": Timestamp, "data": Array of Floats }`
-    - Some values in `data` might be `null` if there is no data available for that time slot
-2. `POST /api/<from>/<to>/stats`
-    - The Request-Body shall be the same as for a `timeseries` query
-    - The response will be a JSON array, each entry in the array corresponding to the selector found at that index in the request's `selectors` array
-    - Each array entry will be a map from every requested metric to this: `{ "from": Timestamp, "to": Timestamp, "samples": Int, "avg": Float, "min": Float, "max": Float }`
-    - If the `samples` value is 0, the statistics should be ignored.
-3. `POST /api/<to>/free`
-    - Request-Body: Array of selectors
-    - This request will free up and release all data older than `to` for all nodes specified by the selectors
-4. `GET /api/{cluster}/peek`
-    - Return a map from every node in the specified cluster to a map from every metric to the newest value available for that metric
-    - All cpu/socket level metrics are aggregated to the node level
-5. `POST /api/write`
-    - You can send lines of the InfluxDB line protocol to this endpoint and they will be written to the store (Basically an alternative to NATS)
+The REST API is documented in [openapi.yaml](./openapi.yaml) in the OpenAPI 3.0 format.
 
 ### Run tests
 
@@ -51,7 +26,7 @@ go test -v ./...
 go test -bench=. -race -v ./...
 ```
 
-### What are these selectors mentioned in the code and API?
+### What are these selectors mentioned in the code?
 
 Tags in InfluxDB are used to build indexes over the stored data. InfluxDB-Tags have no
 relation to each other, they do not depend on each other and have no hierarchy.
@@ -149,23 +124,10 @@ And finally, use the API to fetch some data. The API is protected by JWT based a
 JWT="eyJ0eXAiOiJKV1QiLCJhbGciOiJFZERTQSJ9.eyJ1c2VyIjoiYWRtaW4iLCJyb2xlcyI6WyJST0xFX0FETUlOIiwiUk9MRV9BTkFMWVNUIiwiUk9MRV9VU0VSIl19.d-3_3FZTsadPjDEdsWrrQ7nS0edMAR4zjl-eK7rJU3HziNBfI9PDHDIpJVHTNN5E5SlLGLFXctWyKAkwhXL-Dw"
 
 # If the collector and store and nats-server have been running for at least 60 seconds on the same host, you may run:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/timeseries" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\"]], \"metrics\": [\"load_one\"] }"
-
-# Get flops_any for all CPUs:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/timeseries" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\"]], \"metrics\": [\"flops_any\"] }"
-
-# Get flops_any for CPU 0:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/timeseries" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\", \"cpu0\"]], \"metrics\": [\"flops_any\"] }"
-
-# Get flops_any for CPU 0, 1, 2 and 3:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/timeseries" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\", [\"cpu0\", \"cpu1\", \"cpu2\", \"cpu3\"]]], \"metrics\": [\"flops_any\"] }"
-
-# Stats for load_one and proc_run:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/stats" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\"]], \"metrics\": [\"load_one\", \"proc_run\"] }"
-
-# Stats for *all* CPUs aggregated both from CPU to node and over time:
-curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/$(expr $(date +%s) - 60)/$(date +%s)/stats" -d "{ \"selectors\": [[\"testcluster\", \"$(hostname)\"]], \"metrics\": [\"flops_sp\", \"flops_dp\"] }"
-
+curl -H "Authorization: Bearer $JWT" -D - "http://localhost:8080/api/query" -d "{ \"cluster\": \"testcluster\", \"from\": $(expr $(date +%s) - 60), \"to\": $(date +%s), \"queries\": [{
+  \"metric\": \"load_one\",
+  \"hostname\": \"$(hostname)\"
+}] }"
 
 # ...
 ```
diff --git a/TODO.md b/TODO.md
index a8f37a4..91b2eab 100644
--- a/TODO.md
+++ b/TODO.md
@@ -10,4 +10,5 @@
 - Optimization: Once a buffer is full, calculate min, max and avg
     - Calculate averages buffer-wise, average weighted by length of buffer
     - Only the head-buffer needs to be fully traversed
+- Optimization: If aggregating over hwthreads/cores/sockets cache those results and reuse some of that for new queres aggregating only over the newer data
 - ...
diff --git a/openapi.yaml b/openapi.yaml
new file mode 100644
index 0000000..f33e01d
--- /dev/null
+++ b/openapi.yaml
@@ -0,0 +1,138 @@
+# OpenAPI spec describing a subset of the HTTP REST API for the cc-metric-store.
+
+openapi: 3.0.3
+info:
+  title: 'cc-metric-store REST API'
+  description: 'In-memory time series database for hpc metrics to be used with the [ClusterCockpit](https://github.com/ClusterCockpit) toolsuite'
+  version: 0.1.0
+paths:
+  '/api/write':
+    post:
+      operationId: 'writeMetrics'
+      description: 'Recieves metrics in the influx line-protocol using [this format](https://github.com/ClusterCockpit/cc-specifications/blob/master/metrics/lineprotocol_alternative.md)'
+      requestBody:
+        required: true
+        content:
+          'text/plain':
+            example:
+              'flops_any,cluster=emmy,hostname=e1001,type=cpu,type-id=0 value=42.0'
+      responses:
+        200:
+          description: 'Everything went fine'
+        400:
+          description: 'Bad Request'
+  '/api/query':
+    post:
+      operationId: 'queryMetrics'
+      description: 'Query metrics'
+      requestBody:
+        required: true
+        content:
+          'application/json':
+            schema:
+              type: object
+              required: [cluster, from, to]
+              properties:
+                cluster:
+                  type: string
+                from:
+                  type: integer
+                to:
+                  type: integer
+                with-stats:
+                  type: boolean
+                  default: true
+                with-data:
+                  type: boolean
+                  default: true
+                queries:
+                  type: array
+                  items:
+                    $ref: '#/components/schemas/ApiQuery'
+                for-all-nodes:
+                  description: 'If not null, add a new query for every known host on that cluster and every metric (at node-scope) specified in this array to the request. This can be used to get a metric for every host in a cluster without knowing the name of every host.'
+                  type: array
+                  items:
+                    type: string
+      responses:
+        200:
+          description: 'Requested data and stats as JSON'
+          content:
+            'application/json':
+              schema:
+                description: 'Array where each element is a response to the query at that same index in the request'
+                type: array
+                items:
+                  description: 'If `aggreg` is true, only ever has one element.'
+                  type: array
+                  items:
+                    type: object
+                    properties:
+                      error:
+                        description: 'If not null or undefined, an error happend processing that query'
+                        type: string
+                        nullable: true
+                      data:
+                        type: array
+                        items:
+                          type: number
+                          nullable: true
+                      avg: { type: number }
+                      min: { type: number }
+                      max: { type: number }
+        400:
+          description: 'Bad Request'
+  '/api/free':
+    post:
+      operationId: 'freeBuffers'
+      description: 'Allow all buffers containing only data older than `to`'
+      parameters:
+        - name: to
+          in: query
+          description: 'Unix Timestamp'
+          required: true
+          schema:
+            type: integer
+      requestBody:
+        required: true
+        content:
+          'application/json':
+            schema:
+              type: array
+              items:
+                type: array
+                items:
+                  type: string
+      responses:
+        200:
+          description: 'Everything went fine'
+        400:
+          description: 'Bad Request'
+components:
+  schemas:
+    ApiQuery:
+      description: 'A single query for a specific metric resulting in one series'
+      type: object
+      required: [metric, hostname, aggreg]
+      properties:
+        metirc:
+          type: string
+        hostname:
+          type: string
+        type:
+          description: 'Not required for node-level requests. Usually something like socket, cpu or hwthread.'
+          type: string
+        type-ids:
+          type: array
+          items:
+            type: integer
+        aggreg:
+          type: boolean
+          description: 'If true, every query result will have exactly one element. Otherwise, the data for every requested type-id/sub-type-id is provided seperately'
+  securitySchemes:
+    bearerAuth:
+      type: http
+      scheme: bearer
+      bearerFormat: JWT
+security:
+  - bearerAuth: [] # Applies `bearerAuth` globally
\ No newline at end of file