> ## Documentation Index > Fetch the complete documentation index at: https://proto.evodesign.org/docs/llms.txt > Use this file to discover all available pages before exploring further. # Specific K-mer Frequency > Evaluate frequency or usage deviation of a specific k-mer motif

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Source

evo-design/proto-language/proto\_language/constraint/sequence\_composition/specific\_kmer\_constraint.py

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Constraint contributors

Evaluate frequency or usage deviation of a specific k-mer. Supports two scoring modes: 1. **Frequency mode**: Raw k-mer frequency (count / total k-mer positions). 2. **Usage deviation mode**: Observed/expected ratio using a zero-order Markov model (product of individual character frequencies). Metadata varies by mode: **Frequency mode:** * `{kmer}_frequency`: Float frequency value **Usage deviation mode:** * `{kmer}_usage_deviation`: Float observed/expected ratio * `{kmer}_count`: Integer observed count * `{kmer}_expected`: Float expected count ## API Reference

ConfigSpecificKmerConfig Source

Configuration for evaluating a single specific k-mer. For evaluating all k-mers of a given length, use KmerFrequencyConstraint. The specific k-mer to evaluate (e.g., 'CG', 'GATC', 'ATG') Scoring mode: 'frequency' for raw counts, 'usage\_deviation' for observed/expected ratio Options: `frequency`, `usage_deviation` Minimum acceptable frequency/deviation based on scoring\_mode Maximum acceptable frequency/deviation based on scoring\_mode

ReturnsConstraintOutput

One result per input sequence. The `metadata` field carries per-mode k-mer data (see Note).

## Usage ```python python icon="python" theme={null} from proto_language.core import Constraint from proto_language.constraint import specific_kmer_constraint, SpecificKmerConfig constraint = Constraint( inputs=[segment], function=specific_kmer_constraint, function_config=SpecificKmerConfig( # Configure parameters here ), ) scores = constraint.evaluate() ``` ## Metadata | Property | Value | | --------------- | -------------------------- | | Key | `specific-kmer-frequency` | | Function | `specific_kmer_constraint` | | Category | `sequence_composition` | | Mode | `discrete` | | Uses GPU | `False` | | Supported Types | `dna`, `rna`, `protein` |