# Metrics

The Metrics capability provides WASM function developers the ability to create user-defined metrics exposed as part of the Tarmac `/metrics` end-point. This capability supports the three predominant metrics types, Counters, Gauges, & Histograms.

## Counter

The Counter function will give users the ability to create a custom counter metric. When called, this function will increment the counter by one.

```golang
_, err := wapc.HostCall("tarmac", "metrics", "counter", MetricsCounterJSON)
```

### Interface Details

| Namespace | Capability | Function  | Input            | Output |
| --------- | ---------- | --------- | ---------------- | ------ |
| `tarmac`  | `metrics`  | `counter` | `MetricsCounter` | `nil`  |

### Example JSON

This callback uses JSON messages as input and output to facilitate communications between WASM functions and the Tarmac host.

#### MetricsCounter

```json
{
	"name": "custom_metric_name"
}
```

## Gauge

The Gauge function will give users the ability to create a custom gauge metric. When called, this function will either increment or decrement the gauge by one.

```golang
_, err := wapc.HostCall("tarmac", "metrics", "gauge", MetricsGaugeJSON)
```

### Interface Details

| Namespace | Capability | Function | Input          | Output |
| --------- | ---------- | -------- | -------------- | ------ |
| `tarmac`  | `metrics`  | `gauge`  | `MetricsGauge` | `nil`  |

### Example JSON

This callback uses JSON messages as input and output to facilitate communications between WASM functions and the Tarmac host.

#### MetricsCounter

```json
{
	"name": "custom_metric_name",
	"action": "inc"
}
```

Valid actions are `inc` (Increment) and `dec` (Decrement).

## Histogram

The Histogram function will give users the ability to create a custom histogram metric. When called, this function will observe the provided value and summarize the metric results.

```golang
_, err := wapc.HostCall("tarmac", "metrics", "histogram", MetricsHistogramJSON)
```

### Interface Details

| Namespace | Capability | Function    | Input              | Output |
| --------- | ---------- | ----------- | ------------------ | ------ |
| `tarmac`  | `metrics`  | `histogram` | `MetricsHistogram` | `nil`  |

### Example JSON

This callback uses JSON messages as input and output to facilitate communications between WASM functions and the Tarmac host.

#### MetricsCounter

```json
{
	"name": "custom_metric_name",
	"value": 0.0001
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://tarmac.gitbook.io/tarmac-framework/capabilities/metrics.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.