# Context Counting overview

> Count complete preflight requests with explicit quality and transport trust metadata.

- Path: `Guides > Inference > Context Counting > Overview`
- Human: https://looprig.com/docs/guides/inference/context-counting
- Machine index: https://looprig.com/llms.txt

Context counting is a preflight occupancy seam. It counts the complete
provider-neutral `inference.Request` before invocation so admission policy can
compare input tokens with a model context limit. It is not a response-usage
wrapper and it does not count generated output.

## Purpose

```go
type ContextCount struct {
	Model       model.ModelKey
	InputTokens content.TokenCount
	Quality     CountQuality
}

type ContextCounter interface {
	CountContext(context.Context, inference.Request) (ContextCount, error)
	CounterCapability() CounterCapability
}
```

`InputTokens` is the occupancy of the complete request, including system text,
conversation, tools, structured-output schema, and dialect-specific encoding.
`Quality` distinguishes provider-exact, local-exact, and heuristic estimates.

Harness consumes this preflight result for [context limits](/docs/guides/harness/loop/context-limits.md)
and [automatic compaction thresholds](/docs/guides/harness/compaction/context-thresholds.md).

## Flow

```mermaid
%%{init: {"theme":"base","themeVariables":{"background":"#111827","primaryColor":"#1f2937","primaryTextColor":"#f9fafb","primaryBorderColor":"#60a5fa","lineColor":"#94a3b8","secondaryColor":"#172033","tertiaryColor":"#0f172a","fontFamily":"Inter, ui-sans-serif, system-ui"}}}%%
flowchart LR
    Q["complete Request"] --> C["ContextCounter"]
    C --> M["ContextCount: model, input, quality"]
    M --> A["admission policy"]
    A --> I["invoke or reject"]
    U["response Usage"] -. separate postflight data .-> R["billing/telemetry"]
```

## Source and proof

- [`contextcount/contracts.go`](https://github.com/looprig/inference/blob/v0.12.0/contextcount/contracts.go)
- [`contextcount/estimator.go`](https://github.com/looprig/inference/blob/v0.12.0/contextcount/estimator.go)
- [`contextcount/estimator_test.go`](https://github.com/looprig/inference/blob/v0.12.0/contextcount/estimator_test.go)

Run `go test ./contextcount`.