# Napkin

> The sketchbook for things that have to work. Napkin connects engineering quantities, equations, drawings, assumptions, and checks in a Study.

A .napkin file is readable engineering source. It compiles into the same Study model used by the local plugin, hosted MCP server, and interactive Model/Source views. The website contains 527 executable worked examples across 51 engineering topics. Read each example's implemented scope; the broader topic may require additional equations and evidence.

## Language and documentation

- [Napkin language reference](https://napkin.engineering/spec): Declaration syntax, pi and e, const semantics, built-in functions, unit spellings and conversions, checks, scenarios, geometry, and source-to-Study behavior.
- [Why Napkin](https://napkin.engineering/why): Engineering tools for thought and the purpose of linked sketch models.
- [Editing source](https://napkin.engineering/howto/edit-napkin-source): Edit quantities, equations, and checks in a working example.
- [Workflow guides](https://napkin.engineering/howto): Available how-to articles.

## Calculations and examples

- [Calculator library](https://napkin.engineering/calculators): Browse all engineering topics and source-backed worked examples.
- [Cantilever study](https://napkin.engineering/calculators/cantilever): Editable beam geometry, end-load deflection, checks, and scenario overlays.
- [Mass to weight](https://napkin.engineering/units/force-mass-weight): Weight from mass and explicit gravity.
- [Volumetric to mass flow](https://napkin.engineering/units/flow): Mass flow using volumetric flow and density.
- [Historical examples](https://napkin.engineering/examples): Historical drawings, source credits, and illustrative models.
- [Cantilever source](https://napkin.engineering/sources/structures/beam-deflection.napkin): Executable plain-text example.
- [Flow source](https://napkin.engineering/sources/units/flow.napkin): Executable plain-text example.

Catalog source files are available at /sources/<family>/<slug>.napkin for registered calculator routes. Page edits preview temporary studies and are not saved to an account.

## Agent connection and authentication

- [Connection guide](https://napkin.engineering/connect): Local Codex/Claude Code plugin setup and hosted MCP connection.
- [Agent authentication guide](https://napkin.engineering/auth.md): WorkOS-provided registration and claim instructions. Follow the live guide; do not assume every registration method is enabled.
- [MCP resource metadata](https://napkin.engineering/.well-known/oauth-protected-resource/mcp): OAuth authorization-server discovery for the protected MCP resource.
- [Hosted MCP endpoint](https://napkin.engineering/mcp): Streamable HTTP MCP endpoint; requires an authorized bearer token. An unauthenticated request returns an OAuth challenge, not an engineering result.
- [Repository](https://github.com/workbenchai/napkin/tree/dev): Source, local plugin instructions, and core/React APIs.

For authenticated study edits, inspect capabilities and the current revision. napkin_source validates and applies complete source; napkin_sketch applies additive fragments. Keep source validation distinct from saving a study, and retain the model's stated assumptions and limits when reporting a result.

## Applicability

These are first-order analytical studies, not general dynamic simulations or certified designs. A passing check means its stated mathematical requirement passed. It does not independently verify the physical approximation, supplied material data, or a complete design. General CAD import/export and image-to-part recognition are not shipped. Drawings are available when a model actually declares supported geometric parts; scalar models use numeric scenario comparisons.