ContextWindowEstimator

Namespace AgentPrism · Assembly AgentPrism.Core.dll

Estimates a prompt’s token count and whether it would be rejected by the pre-flight context-window check, without calling a model provider.

public sealed class ContextWindowEstimator

Inheritance

object ← ContextWindowEstimator

Inherited Members

object.GetType(), object.ToString(), object.Equals(object?), object.Equals(object?, object?), object.ReferenceEquals(object?, object?), object.GetHashCode()

Remarks

The estimate is approximate: counting is done with a single fixed OpenAI encoding (o200k_base, via Tokenizers.TiktokenTokenizer) regardless of the bound provider — Anthropic and Google publish no equivalent offline tokenizer package. The count is close enough to size a prompt against a context window; it is not the exact count any specific provider would bill.

The tokenizer is built ONCE and reused: constructing one loads the vocab data package’s contents, and doing that per call would make even a cheap estimate expensive.

Constructors

ContextWindowEstimator(IModelProviderRegistry, IOptionsMonitor<AgentPrismOptions>)

Creates a new estimator.

public ContextWindowEstimator(IModelProviderRegistry registry, IOptionsMonitor<AgentPrismOptions> optionsMonitor)

Parameters

registry IModelProviderRegistry

The registry used to look up the model’s context window.

optionsMonitor IOptionsMonitor<AgentPrismOptions>

The runtime settings, for AgentPrismPreflightOptions.ReserveRatio.

Exceptions

ArgumentNullException

A dependency is null.

Methods

Estimate(ModelBinding, string?)

Estimates prompt against binding’s context window.

public ContextWindowEstimate Estimate(ModelBinding binding, string? prompt)

Parameters

binding ModelBinding

The model binding whose context window applies.

prompt string?

The prompt text to count. Empty when null.

Returns

ContextWindowEstimate

The estimate.

Exceptions

ArgumentNullException

binding is null.