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.
Borrowing it
Nothing to install: this file belongs to JetBrains/MPS. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/JetBrains/MPS/master/.agents/skills/mps-aspect-actions/SKILL.mdgit 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-actions)<a href="https://agentmods.dev/skills/jetbrains/mps/mps-aspect-actions"><img src="https://agentmods.dev/badge/skills/jetbrains/mps/mps-aspect-actions.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 | $0.00115 | $0.01786 |
| Opus 5 | $0.00057 | $0.00893 |
| Sonnet 5 | $0.00023 | $0.00357 |
| Haiku 4.5 | $0.00012 | $0.00179 |
Grade A, and why
mps-aspect-actions 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 7d 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 — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MPS Actions Aspect
The actions aspect customizes how new nodes of a concept are constructed by the MPS editor — typically during substitution, side transformations, right-transform/<ctrl-space> replacement, or auto-replace. The framework produces an empty instance of the target concept; the setup function then populates it, often copying fields from the node it is replacing (sampleNode). Lives in <lang>/models/<lang>.actions.mps, language jetbrains.mps.lang.actions. The aspect also hosts copy/paste handlers and paste wrappers (see references/copy-paste-and-paste-wrappers.md).
Critical Directives
- One
NodeFactoriesroot per actions model; add per-conceptNodeFactorychildren to it. Do not create one root per concept. - One
NodeFactoryperapplicableConcept. Multiple factories for the same concept are not merged. - The setup function runs before
newNodeis attached to the model.newNode.parent, ancestors, and model-wide queries return null/empty. Use theenclosingNodeimplicit parameter when you need the would-be parent. sampleNodeis typed asnode<BaseConcept>. Always narrow withifInstanceOf (sampleNode is <Concept> original)before accessing fields — direct dereference will NPE or fail to compile.- Use
SPropertyAccess(refproperty→PropertyDeclaration) for properties; useSLinkAccess(reflink→LinkDeclaration) for both containment and reference child roles. - Factories do not fire for quotations
<C()>,model.add root(<C()>),model.add new root(C), or pure rendering. If you need factory-initialised nodes in generator code, usenew node<C>()with explicit property assignments or route creation through an intention that callsadd new initialized. - Edit factories through MPS MCP tools (
mps_mcp_insert_root_node_from_json,mps_mcp_update_node, optionallymps_mcp_parse_java_and_insertwithfeatureKind: "STATEMENTS"for the body). Do not hand-edit.mpsfiles. - After editing, validate with
mps_mcp_check_root_node_problemson theNodeFactoriesroot and rebuild the language.
What ships with it
6 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.
- 7d ago First seen · 59 lines · 115 tokens per session scan A 1c89893abb5b
mps-aspect-actions is a skill published in the GitHub repository JetBrains/MPS (1,656 stars, last pushed yesterday), licensed Apache-2.0. It adds 115 tokens to every session and 1,786 once invoked, about $0.0006 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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