JetBrains MPS is a development environment for creating domain-specific languages, which are programming languages designed for a particular field or task. It provides editors with features such as completion, semantic checks, and type checking, and can generate code in languages including Java and XML.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/jetbrains/mps/mps-aspect-editornpx skills add JetBrains/MPS --skill mps-aspect-editorgit clone --depth 1 https://github.com/JetBrains/MPSWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/jetbrains/mps/mps-aspect-editor)<a href="https://agentmods.dev/skills/jetbrains/mps/mps-aspect-editor"><img src="https://agentmods.dev/badge/skills/jetbrains/mps/mps-aspect-editor.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00179 | $0.01805 |
| Opus 5 | $0.00089 | $0.00903 |
| Sonnet 5 | $0.00036 | $0.00361 |
| Haiku 4.5 | $0.00018 | $0.00180 |
Grade A, and why
mps-aspect-editor scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 53 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MPS Editor — Technical Reference
The jetbrains.mps.lang.editor language defines projectional editors as trees of cell models (display elements) with cell layouts and style items. This skill is the technical lookup: concept names, suffixes, style classes, and the rules that decide which cell model to use where.
Critical Directives
- Always use
CellModel_RefNodeListfor0..nor1..nchildren.CellModel_RefNodeis for single cardinality only. - Use
IndentLayoutOnNewLineStyleClassItem(apply to the cell that should start on a new line) instead of the legacyIndentLayoutNewLineStyle(applied to the cell before the break) — the latter is easier to get wrong. - Reference cells: set the internal
CellModel_Property(e.g.name) inside anInlineEditorComponenttoreadOnly=trueso the referenced target cannot be accidentally renamed through the editor. - Smart references: no wrapping layout cell — just a single
CellModel_RefCellwhoseeditorComponentis anInlineEditorComponentwith aCellModel_Property(relationDeclaration: name,readOnly: true). - List empty state: a
CellModel_RefNodeListalready synthesizes an editable empty cell (caret lands there,Ctrl+Spaceworks). Add an explicitemptyCellModel(e.g. aCellModel_Constant "<no items>") only to customize the empty cell — but a plain constant is read-only and loses the instant-typing, so to keep it, put the hint in the constant'snullText(nottext) and add anEditableStyleClassItem(flag=true). See the Editable Empty-List Placeholder pattern inreferences/editor-patterns.md. - Inheritance: components can be reused if defined for the concept, its super-concepts, or implemented interfaces.
- Componentize shared cells: when several concept editors repeat the same cell group, factor it into an
EditorComponentDeclaration(bound to the most general concept or interface that owns the relations) and reuse it viaCellModel_Component. Seereferences/editor-components.md. - Stylesheets: check for existing style classes in extended languages before creating new ones in a
StyleSheetnode.
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 53 lines · 179 tokens per session scan A 4b5bfb4a8d16
mps-aspect-editor is a skill published in the GitHub repository JetBrains/MPS (1,658 stars, last pushed today), licensed Apache-2.0. It adds 179 tokens to every session and 1,805 once invoked, about $0.0009 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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