# Visualization API

Every shading mode and colormap described elsewhere in this documentation - magnitude, sparsity-mask, quantization boundaries, the diverging cyan/red/dark diff convention - is an instance of the same underlying extension point: a **`TensorMetric`**, which computes a value per tile and a way to render it.

## What a `TensorMetric` provides

-   **A statistic function** - computed the same [mergeable, monoid](/docs/inspect-and-analyze/tensor-statistics#why-mergeable-matters) way as Tensormorph's built-in tile statistics, so a custom metric gets [level-of-detail streaming](/docs/core-concepts/level-of-detail-and-streaming) for free rather than needing its own caching strategy.
-   **A color mapping** - how a computed value becomes a color in the [Matrix and Heatmap](/docs/editors/matrix-and-heatmap-editor) and [Architecture](/docs/editors/architecture-editor) shading-mode lists.
-   **A scale** - linear, log, or diverging around a meaningful zero point, matching whichever is appropriate for what the metric measures.

Implementing the mergeable-statistic contract correctly is what makes a custom metric behave like a built-in one - available at every zoom level, computed once and reused, rather than recomputed per view or unavailable at coarse levels of detail.

## A worked example

A plugin adding a domain-specific metric - say, a custom interpretability score computed per-weight - registers a `TensorMetric` that: computes the score per tile in a mergeable form, maps it to a color scale (likely diverging, if the score has a meaningful positive/negative/neutral structure), and from that point on appears as an ordinary shading-mode option everywhere shading modes are selectable, without any per-view integration work.

## Custom colormaps without a new metric

A `TensorMetric` isn't required just to add a colormap for an *existing* statistic - see [Settings](/docs/reference/settings#common-settings-areas) for swapping the colormap used by a built-in shading mode, which doesn't require plugin code at all.

## Related resources

-   [Tensor Statistics](/docs/inspect-and-analyze/tensor-statistics) - the mergeable-statistic contract a custom metric must satisfy.
-   [Matrix and Heatmap Editor](/docs/editors/matrix-and-heatmap-editor) - the diverging-color convention a metric's scale should follow where applicable.
-   [Extension API](/docs/developer-platform/extension-api) - the plugin ABI a `TensorMetric` is registered under.