What is mps-aspect-migrations?

Instructions for writing migration scripts in JetBrains MPS, a tool for defining programming languages and their models. These scripts update existing user models after a language's concepts, links, properties, or structure change.

Use it to move or rename concepts, change containment or reference links, update properties and children, remove concepts, order migration steps, and version-gate model upgrades.

They clarify which migration mechanism fits a structural change and which fits changing existing model content. This helps prevent versioning mistakes and confusion between similarly named MPS concepts.

How JetBrains/MPS configures Claude Code and Codex

About the project

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.

JetBrains/MPS · 1,657 stars · on GitHub · jetbrains.com

Reuse

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.

Copy the file

curl -O https://raw.githubusercontent.com/JetBrains/MPS/master/.agents/skills/mps-aspect-migrations/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/JetBrains/MPS

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/jetbrains/mps/mps-aspect-migrations.svg)](https://agentmods.dev/skills/jetbrains/mps/mps-aspect-migrations)

Your own site

<a href="https://agentmods.dev/skills/jetbrains/mps/mps-aspect-migrations"><img src="https://agentmods.dev/badge/skills/jetbrains/mps/mps-aspect-migrations.svg" alt="Measured on agentmods" height="20"></a>

Per session 145 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,369 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

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	$0.00145	$0.01369
Opus 5	$0.00072	$0.00685
Sonnet 5	$0.00029	$0.00274
Haiku 4.5	$0.00015	$0.00137

Measured 8d ago against content hash 68798358304c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

mps-aspect-migrations 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 8d 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.

.agents/skills/mps-aspect-migrations/SKILL.md · 50 lines

How it starts

The opening of the file, as written. The whole thing — 50 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MPS Migrations Aspect

Two complementary languages upgrade user models when language definitions change:

jetbrains.mps.lang.migration (l:90746344-04fd-4286-97d5-b46ae6a81709) — core migration language with MigrationScript (class-based, programmatic) and PureMigrationScript (declarative, structural).
jetbrains.mps.lang.script (l:0eddeefa-c2d6-4437-bc2c-de50fd4ce470) — Enhancement Scripts that apply concept-instance transformations, used for richer per-node updates.

These address the same problem at different abstraction levels: lang.migration handles structural language refactorings (concept moves/renames, removed concepts); lang.script handles content transformations (modifying properties, children, references of existing instances).

Critical Directives

Do not confuse the two MigrationScript concepts. One is in lang.migration (BL ClassConcept, version-gated). The other (alias "Enhancement Script") is in lang.script (instance-level transformer). Always disambiguate by language ref.
fromVersion is the version migrated FROM, not to. Bump the language's version integer in the .mpl solution manifest whenever you add a migration step.
Model naming is convention-driven and load-bearing. lang.migration scripts live in <language.fqn>.migration. lang.script Enhancement Scripts live in <language.fqn>.scripts. MPS discovers them by these names at startup.
Migration scripts run in dependency order, determined by OrderDependency / ExecuteAfterDeclaration. Always declare ordering when the result of one script feeds the next.
Do not hand-edit serialized .mps migration files. Use MPS MCP node tools.

Workflow

Decide form: PureMigrationScript for structural moves/renames/removals; MigrationScript for programmatic transforms; Enhancement Script for instance-level updates. See references/form-selection.md.
Create or locate the migration model with mps_mcp_create_model: <language.fqn>.migration for lang.migration (aspect ID migration); <language.fqn>.scripts for Enhancement Scripts (aspect ID scripts). Both aspect IDs are case-sensitive and carry no @ suffix — see aspect-model-stereotypes.md. Add the used languages required for that form.
Bump the language version integer in the .mpl and set fromVersion on the new script to the previous version.
Build the script body (declarative parts, BL execute() method, or MigrationScriptPart_Instance updater) using the JSON blueprints in references/json-blueprints.md.
Wire ordering (OrderDependency / ExecuteAfterDeclaration) and data flow (putData / getData) if needed.
Validate via mps_mcp_check_root_node_problems, then run the migration on a test model.

Read the full file on GitHub · 50 lines

Files

What ships with it

8 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.

Changes

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.

8d ago First seen · 50 lines · 145 tokens per session scan A 68798358304c

Subscribe to this mod's changes

mps-aspect-migrations is a skill published in the GitHub repository JetBrains/MPS (1,657 stars, last pushed today), licensed Apache-2.0. It adds 145 tokens to every session and 1,369 once invoked, about $0.0007 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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