Arc

Step-by-step guidance for building a React page in a Cratis Arc application — listing data with DataPage, toolbar actions with CommandDialog, row selection, detail panels, observable queries, and MVVM. Use whenever building or modifying a React page that lists or displays data, adding a table or grid, wiring up Add/Edit/Delete actions, using DataPage, DataTableForQuery, CommandDialog, or any @cratis/components. Also trigger when connecting a React component to a proxy-generated query or observable query.

Use this skill when asked to add a Chronicle reactor (automation or translation) to a Cratis-based project. Reactors observe events and produce side effects.

Diátaxis Documentation Expert for Cratis projects. Writes high-quality DocFX documentation guided by the Diátaxis framework — classifying every page as a Tutorial, How-to Guide, Reference, or Explanation.

Use this skill when changing, fixing, or improving Cratis documentation whose source file is under `Documentation/**` in a product or contributing repo. The content is split across repos (each product owns its docs in its own `Documentation/` folder; the `Documentation` repo aggregates them), so this skill finds the real source file, edits it, syncs, and verifies. Trigger whenever someone asks to edit/update/fix/reword a docs page, fix a broken link, correct a code example, update a guide or tutorial or reference page, or says a docs page is wrong/outdated — for Chronicle, Arc, Components, CLI, Fundamentals, or the contributing docs.

Use this skill to visually QA rendered docs site pages after changes to source files under `Documentation/**` — screenshot pages headless in light AND dark, evaluate how they look against the aspire.dev bar, check diagrams/tables/code blocks render, and diagnose layout-shift ("flicker"/"twitch"/"pop") bugs. Trigger when someone asks to screenshot the docs, check how a docs page looks, review the docs visually, verify a diagram or table renders, compare the docs to aspire.dev, or investigate a flicker/jump/layout-shift on the docs site.

Use this skill when creating a NEW Cratis documentation page under `Documentation/**` in a product or contributing repo — a new tutorial chapter, how-to/guide, explanation/concept page, reference page, or scenario/recipe. Handles where the file goes (which product repo), wiring it into the sidebar nav (toc.yml + Diátaxis bucket), and verifying it renders. Trigger when someone asks to add/create/write a new docs page, document a new feature, add a guide/tutorial/recipe/concept to the docs, or add a new section to a product's documentation.

Use this skill when asked to add a validation rule, business rule, or uniqueness constraint to an existing command in a Cratis-based project.

Use this skill when asked to create a strongly-typed domain identifier or value (such as ProjectId, AuthorName, InvoiceNumber) in a Cratis-based project. Produces a ConceptAs<T> record with the correct conversions and sentinel values.

Use this skill when asked to add a database table, column, relationship, or other schema change via Entity Framework Core in a Cratis-based project.

Use this skill when asked to add a Chronicle projection to a Cratis-based project. Favor model-bound projections by default, and only fall back to declarative/fluent `IProjectionFor<T>` projections when model-bound attributes cannot express the behavior cleanly. Enforces the AutoMap-first rule and Chronicle-specific join semantics.

Use this skill when asked to set up authentication, authorization, or identity in a Cratis Arc project — backend, frontend, or both. Covers implementing identity providers, protecting commands/queries with authorization attributes, integrating Microsoft Identity Platform, connecting backend identity to React frontends, and local development testing with generated principals. Also covers customizing IProvideIdentityDetails for enriching identity from databases, blocking users, multi-tenant identity, user preferences, and modifying identity at runtime. Use this whenever the user mentions auth, login, roles, permissions, identity details, user context, protecting endpoints, identity provider customization, or anything related to who the user is and what they can access.

Step-by-step guidance for creating a Cratis Arc command — [Command] record, Handle() method, CommandValidator, proxy generation, and React .use() hook with CommandDialog. Use when adding or creating a command, wiring up a form or button to the backend, working with IEventLog, CommandResult, CommandValidator, CommandDialog, or [Command] attribute.

Reference for Cratis C# coding conventions — formatting, naming, records, nullable handling, exceptions, logging, and DI. Use whenever writing C# in a Cratis project, deciding between record vs class, checking naming rules, applying formatting conventions, handling null safety, creating exception types, or asking "how should this be written?" Also covers CUPID characteristics and domain-based folder structure. Trigger on any C# style or standards question for a Cratis project.

Step-by-step guidance for creating a Cratis Chronicle read model from scratch — defining events, choosing between projection and reducer, [ReadModel] record with static query methods, and the generated TypeScript proxy in React. Use when creating a read model, working with [EventType], [ReadModel], IProjectionFor, IReducerFor, observable queries, or deriving state from events. For adding a projection or reactor to an existing read model, use add-projection instead.

Step-by-step guidance for writing C# specs in Cratis using BDD-style Specification by Example — the Establish/Because/should_ pattern, for_/when_/and_ folder hierarchy, reusable given/ contexts, NSubstitute mocking, and Chronicle integration specs. Use when writing C# unit or integration specs, creating spec files or folders, structuring the for_<Type>/when_<behavior>/and_<condition> hierarchy, mocking with NSubstitute, writing given/ reusable contexts, or using ShouldEqual/ShouldBeTrue assertions. For integration specs specifically tied to a vertical slice command, write-specs offers a more focused workflow.

Explains how vertical feature slices are structured in a Cratis Chronicle + Arc application — folder layout, what goes in the single backend .cs file, the four slice types (State Change/View/Automation/Translation), and how features compose slices. Use when asking how vertical slices work, where to put files, how to organize a feature folder, which slice type to choose, or how the workflow from C# to TypeScript proxies to React looks. For actively building a new slice end-to-end right now, use new-vertical-slice instead.

Use this skill when asked to implement a new feature, command, query, slice, or screen in a Cratis-based project. Guides the full end-to-end workflow: C# backend → specs → dotnet build → React frontend → quality gates.

Use this skill when asked to review, check, or validate code in a Cratis-based project. Produces a structured review report with blocking issues and suggestions, checked against all project architecture and style standards.

Use this skill when asked to check for performance issues, inefficiencies, or scalability problems in a Cratis-based project. Covers Chronicle projections, MongoDB query patterns, .NET allocations, and React render overhead.

Use this skill when asked to perform a security review or security audit of code in a Cratis-based project. Checks for injection, auth/authz, data exposure, secrets, and event-sourcing-specific vulnerabilities.

Use this skill when asked to create a new feature, section, or page that does not yet exist in a Cratis-based project. Sets up the folder, composition page, routing, and navigation entry before any slices are added.

Ship staged or unstaged local changes: create a branch, make logical commits, push to origin, open a PR with the correct description and label, merge it, and delete the branch locally and on origin. Use whenever the user asks to commit, push, create a PR, ship, or land changes.

Create new skills, modify and improve existing skills, and measure skill performance. Use when users want to create a skill from scratch, update or optimize an existing skill, run evals to test a skill, benchmark skill performance with variance analysis, or optimize a skill's description for better triggering accuracy.

Step-by-step guidance for building a multi-step wizard dialog (StepperCommandDialog) in a Cratis Arc application. Use whenever a command requires gathering information across multiple steps, implementing a wizard flow, breaking a complex form into named stages, or using StepperCommandDialog, StepperPanel, validateOnInit, or wizard-style navigation.

Use this skill when asked to add or build a canvas-style icon toolbar using the @cratis/components Toolbar component. Covers Toolbar, ToolbarButton, ToolbarSeparator, ToolbarSection, ToolbarContext, and ToolbarFanOutItem. Use whenever building tool panels, drawing tool selectors, zoom controls, or any icon-button group with active states, context switching, or fan-out sub-panels.

Use this skill when asked to write tests or specs for event appending, event log behavior, constraint violations, or concurrency violations using EventScenario in a Cratis-based project. Produces infrastructure-free in-process specs using EventScenario and AppendResult Should* extensions.

Use this skill when asked to write tests or specs for read model projections, reducers, or model-bound projections using ReadModelScenario in a Cratis-based project. Produces infrastructure-free in-process specs using ReadModelScenario<TReadModel>.

Use this skill when asked to write tests, specs, or test coverage for a command, query, or slice in a Cratis-based project. Produces BDD-style integration specs using xUnit and Cratis.Specifications.