# Mps Language Aspects Overview

> Entry point for authoring or modifying an MPS language — index of all aspects (structure, editor, constraints, behavior, typesystem, intentions, actions, generator, textgen, accessories, generation plans), the recommended authoring order, cross-aspect call patterns, dependency/rebuild rules, and validation flow. Start here when defining a new language or when you do not know which aspect-specific skill applies.

- Skill: `jetbrains/mps-language-aspects-overview` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jetbrains/mps-language-aspects-overview`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jetbrains/mps-language-aspects-overview/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jetbrains (https://skillmd.com/u/jetbrains)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/jetbrains/mps-language-aspects-overview

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# MPS Language Aspects — Overview

An MPS language is a collection of **aspects**, each a separate model inside the language module. Together they define syntax, semantics, UI, and output. Edit each aspect through its own language (its DSL). This skill is the router; each aspect links to a dedicated skill.

## Critical Directives

- **Always prefer MPS MCP tools over hand-editing `.mps` XML.** Hand edits can silently corrupt model files.
- **Keep aspect rules thin and declarative** — push logic into **behavior methods**, then call them from any aspect.
- **When something in a consumer is wrong, re-check the root cause on the language side** (structure / generator / typesystem) before patching generated Java.
- **Choose a modularity strategy before authoring** when this language must relate to others — reference, extend, embed, or adapt them. The kind you pick (referencing / extension / reuse / embedding) changes how you use structure, constraints, typesystem, and generator. See [`mps-language-modularity`](../mps-language-modularity/SKILL.md).

## Aspects and Where to Find Detailed Guidance

| Aspect | Aspect ID / Stereotype | Model file | Language DSL | Detailed skill |
|---|---|---|---|---|
| **Structure** | `structure` | `models/structure.mps` | `jetbrains.mps.lang.structure` | [`mps-aspect-structure-concepts`](../mps-aspect-structure-concepts/SKILL.md) |
| **Editor** | `editor` | `models/editor.mps` | `jetbrains.mps.lang.editor` | [`mps-aspect-editor`](../mps-aspect-editor/SKILL.md), [`mps-aspect-editor-menus-and-keymaps`](../mps-aspect-editor-menus-and-keymaps/SKILL.md) |
| **Constraints** | `constraints` | `models/constraints.mps` | `jetbrains.mps.lang.constraints` | [`mps-aspect-constraints`](../mps-aspect-constraints/SKILL.md) |
| **Behavior** | `behavior` | `models/behavior.mps` | `jetbrains.mps.lang.behavior` | [`mps-aspect-behavior`](../mps-aspect-behavior/SKILL.md) |
| **Typesystem & Checking** | `typesystem` | `models/typesystem.mps` | `jetbrains.mps.lang.typesystem` | [`mps-aspect-typesystem`](../mps-aspect-typesystem/SKILL.md) |
| **Intentions** | `intentions` | `models/intentions.mps` | `jetbrains.mps.lang.intentions` | [`mps-aspect-intentions`](../mps-aspect-intentions/SKILL.md) |
| **Actions** | `actions` | `models/actions.mps` | `jetbrains.mps.lang.actions` | [`mps-aspect-actions`](../mps-aspect-actions/SKILL.md) |
| **Generator** | `@generator` (stereotype) | `generator/template/main@generator.mps` | `jetbrains.mps.lang.generator` | [`mps-aspect-generator`](../mps-aspect-generator/SKILL.md) |
| **TextGen** | `textGen` | `models/textGen.mps` | `jetbrains.mps.lang.textGen` | [`mps-aspect-textgen`](../mps-aspect-textgen/SKILL.md) |
| **Dataflow** | `dataFlow` (camelCase) | `models/dataFlow.mps` | `jetbrains.mps.lang.dataFlow` | [`mps-aspect-dataflow`](../mps-aspect-dataflow/SKILL.md) |
| **Migrations** | `migration` | `models/migration.mps` | `jetbrains.mps.lang.migration` | [`mps-aspect-migrations`](../mps-aspect-migrations/SKILL.md) |
| **Enhancement scripts** | `scripts` | `models/scripts.mps` | `jetbrains.mps.lang.script` | [`mps-aspect-migrations`](../mps-aspect-migrations/SKILL.md) |
| **Find Usages** | `findUsages` (camelCase) | `models/findUsages.mps` | `jetbrains.mps.lang.findUsages` | — |
| **Refactorings** | `refactorings` | `models/refactorings.mps` | `jetbrains.mps.lang.refactoring` | — |
| **IDE plugin** | `plugin` | `models/plugin.mps` | `jetbrains.mps.lang.plugin` | [`mps-ide-plugin`](../mps-ide-plugin/SKILL.md) |
| **Feedback** | `feedback` | `models/feedback.mps` | `jetbrains.mps.lang.feedback` | — |
| **Accessories / Dependencies** | — (no model created) | `.mpl` and per-model | — | [`mps-aspect-accessories`](../mps-aspect-accessories/SKILL.md) |
| **Code inside bodies** | — | any aspect that holds BL | `baseLanguage`, `smodel`, `collections`, `closures` | [`mps-model-manipulation`](../mps-model-manipulation/SKILL.md) |
| **Inline node literals** | — | any aspect using quotations | `jetbrains.mps.lang.quotation` | [`mps-quotations`](../mps-quotations/SKILL.md) |

Aspect IDs are **case-sensitive** and create models named `<langModule>.<aspectId>` with **no `@` suffix**. Stereotypes (`@generator`, `@genplan`, `@tests`, `@descriptor`) are a separate mechanism for non-aspect models. Authoritative table with usage notes and pitfalls: [aspect-model-stereotypes.md](../mps-mcp-workflow/references/aspect-model-stereotypes.md).

Additional aspects exist (Find Usages, Refactorings, Scopes Provider, Plugin). They follow the same "per-concept rule root + body" pattern — consult companion skills in `.agents/skills/` or the MPS user guide when needed.

**Generation Plans** (cross-cutting, not an aspect of a single language) are covered by [`mps-aspect-generation-plan`](../mps-aspect-generation-plan/SKILL.md). Use when you need to control generator ordering, enable cross-model reference resolution with checkpoints, fork generation into parallel branches, or conditionally contribute plans via `PlanContribution`.

## Typical Authoring Order

1. **Structure** — concepts, properties, children, references, inheritance.
2. **Editor** — notation, cell layouts, projections; iterate alongside sample models.
3. **Constraints** — property validators, reference scopes, placement rules.
4. **Behavior** — concept methods/constructors; callable from any aspect.
5. **Typesystem & checking** — types, subtyping, semantic errors with quick fixes.
6. **Intentions** — alt-enter refactorings and shortcuts.
7. **Generator** — transform to a target language (often BaseLanguage).
8. **TextGen** — only if the target is plain text the language itself emits.
9. **Accessories / runtime / dependencies** — wire into the `.mpl`, ensure consumers can find everything.

Most iteration is circular: structure ↔ editor ↔ constraints ↔ typesystem.

## Cross-Aspect Calls

- Any aspect body can call **behavior methods** on nodes (`node.m(...)`).
- Typesystem rules call **quick-fix intentions** via `error ... fix { ... }` or by referencing `QuickFix` roots.
- Generator templates call **behavior methods** for nontrivial logic and use **mapping labels** for cross-template references.
- Constraints may call **behavior methods** for reusable checks.
- Editors may call **behavior methods** in query/if/cell-model blocks.

Keep logic in behavior methods; keep aspect rules thin and declarative.

## MCP Tools You'll Use Often

- **Exploration**: `mps_mcp_get_project_structure`, `mps_mcp_search_concepts`, `mps_mcp_get_concept_details`, `mps_mcp_print_node`.
- **Authoring**: `mps_mcp_create_root_node`, `mps_mcp_insert_root_node_from_json`, `mps_mcp_update_node`, `mps_mcp_parse_java_and_insert`.
- **Structure-specific**: `mps_mcp_alter_structure` (CREATE_CONCEPTS, CREATE_ENUM, UPDATE_CONCEPT_*), `mps_mcp_query_structure` (inheritance/aspect queries); example nodes of a concept via `mps_mcp_query_nodes` (FIND_INSTANCES).
- **Modules/models**: `mps_mcp_create_module`, `mps_mcp_create_model`, `mps_mcp_model_dependency`, `mps_mcp_model_used_language`, `mps_mcp_module_dependency`.
- **Validation**: `mps_mcp_check_root_node_problems`, language/module build via IDE MCP.

## Dependencies and Rebuilds

After adding/changing:
- **Concepts (structure)** — downstream aspects' references by concept may break; validate them. Rebuild language.
- **Behavior method signatures** — all callers (generator, typesystem, constraints, intentions, editor queries) must be re-validated. Rebuild language.
- **Generator templates** — rebuild generator module (it's separate from the language module).
- **Runtime solutions** — rebuild the runtime solution; consumers pick up changes on next regeneration or reload.
- After large changes: `mps_mcp_reload_all` to refresh MPS's runtime concept registry.

## Validation Flow

1. `mps_mcp_check_root_node_problems` on edited roots / aspect models — catches concept-level problems.
2. Build the language module (IDE MCP) — catches compile errors in generated descriptors.
3. Regenerate a sample model — catches generator/textgen issues.
4. Inspect sample in MPS UI — catches editor / usability issues.

When something in a consumer is wrong, always re-check the root cause on the language side (structure / generator / typesystem) before patching generated Java.