mps-node-editing

name: mps-node-editing description: Add, update, or delete MPS nodes using JSON blueprints — covers the unified blueprint format, staged construction for large subtrees, validation, and reference repair. Use whenever creating, editing, or restructuring nodes in any MPS model (structure, editor, behavior, generator, application code, etc.). type: reference

MPS Node Editing

The core workflow for mutating MPS nodes through MCP tools. JSON blueprints describe the node hierarchy you want; the tools resolve concepts, references, and used languages on insert.

Critical Directives

Always use the fully qualified concept name in the concept field — it is unambiguous and does not require a conceptReference.
Resolve before editing — call mps_mcp_get_current_editor_root_node (for the user's focus) or mps_mcp_search_root_node_by_name (by name) to lock onto the target. Don't guess refs.
Prefer surgical edits — mps_mcp_update_node (ADD/CHILD or SET/CHILD) preserves persistent IDs. mps_mcp_update_root_node_from_json rewrites the entire root and is wasteful when only one subtree changed.
Don't delete-and-reinsert to make a small change — deletion destroys persistent IDs and breaks incoming references.
Validate frequently — call mps_mcp_check_root_node_problems immediately after inserting or modifying a complex node. "ok": true from insert does not mean the AST is semantically valid.

`mps_mcp_update_node` — Unified Node-Mutation Tool

All child, property, and reference operations on existing nodes go through mps_mcp_update_node. The operation is selected via operation (ADD/SET/DELETE) × kind (CHILD/PROPERTY/REFERENCE).

operation × kind	Required parameters	Notes
`ADD` × `CHILD`	`nodeReference` (parent), `childRole`, `childJson`	Optional `position` (0-based; null/-1 = append) and `dryRun`. A `position` ≥ the current child count clamps to an append; a negative value other than -1 is rejected. The response's `data.index` reports the actual landing index.
`SET` × `CHILD`	`childNodeRef`, `childJson`	Replaces an existing child; preserves its position in the role. Optional `dryRun`.
`DELETE` × `CHILD`	`childNodeRef`	Removes the child from its parent.
`SET` × `PROPERTY`	`properties` = `[[nodeRef, propertyName, value], …]`	Batch operation; returns per-row results.
`DELETE` × `PROPERTY`	`nodeReference`, `propertyName`	Clears a single property.
`SET` × `REFERENCE`	`references` = `[[nodeRef, role, targetRefOrName], …]`	Batch operation; `targetRefOrName` accepts an `r:...` ref or a plain name. A plain name is resolved within the reference role's search scope; if it cannot be resolved the call fails (`NOT_FOUND`), preserves the previous reference value, and stores no dangling reference.
`DELETE` × `REFERENCE`	`nodeReference`, `referenceRole`	Clears a single reference.

ADD × PROPERTY and ADD × REFERENCE are not valid combinations and return an error envelope.

mps_mcp_update_node (PROPERTY / REFERENCE / CHILD) and mps_mcp_alter_nodes MOVE_CHILD / MOVE_NODE_TO_PARENT also work on nodes inside the current MPS Console input command — pass the node's normal persistent reference; no extra parameter is needed. The node must be inside the current unexecuted console input (not history/stale). MOVE_NODE_TO_PARENT only relocates a node within the current console command — moving a node between the console and a project model, or making a console node a root, is refused. Edits to console nodes skip disk-persistence and refresh the console's imports instead. Nodes outside the selected project are rejected as before.

childJson accepts either an inline JSON string (max 4 KB) or an absolute path to a file containing the JSON blueprint. Use the file form for large blueprints to avoid MCP-transport truncation.

Prerequisites

Load the mps-language-analysis skill if you do not yet know what concepts the model uses.
Resolve the target node (unless creating a brand-new root):
- mps_mcp_get_current_editor_root_node for the user's focus.
- mps_mcp_search_root_node_by_name for a known name.
Resolve required languages and concepts:
- Check used languages of the current model via mps_mcp_get_project_structure.
- Get concept details using mps_mcp_get_concept_details for specific languages.
- Use mps_mcp_search_concepts for discovery.

Common Workflow

Identify the target node (existing) or parent model (new root).
Choose the right tool: mps_mcp_create_root_node / mps_mcp_insert_root_node_from_json for new roots; mps_mcp_update_node (ADD/SET/DELETE × CHILD/PROPERTY/REFERENCE) for surgical edits; mps_mcp_update_root_node_from_json only for full-root rewrites.
Author the JSON following the unified blueprint format.
Insert with dryRun: true first if the blueprint is large. Check the response: an empty warnings array means staging was clean; a non-empty list means the production write will produce dynamic (unresolved) references for the listed targets — resolve those first or expect broken refs.
Validate with mps_mcp_check_root_node_problems.
Repair broken refs with mps_mcp_alter_nodes FIX_REFERENCES if validation surfaces resolvable-but-unresolved targets.

Related Skills

mps-aspect-structure-concepts — defines what concepts exist and what roles they expose.
mps-baselanguage — when the nodes you edit are BaseLanguage / Java.
mps-quotations — embedding inline node literals inside model code.
mps-language-analysis — exploring an unfamiliar language before editing.
mps-model-manipulation — when the edit also requires navigating the tree from model code (.ancestor<C>, .descendants<C>, siblings, containingRoot).

JSON Input — File-Path Semantics

The tools that accept a node JSON blueprint (mps_mcp_update_node for ADD/SET × CHILD, mps_mcp_insert_root_node_from_json, mps_mcp_update_root_node_from_json) all use the same childJson / json parameter convention:

The parameter can be either a JSON string (max 4 KB) or an absolute path to a local file containing the JSON.
Files may contain either a raw node blueprint or the full MCP response envelope produced by mps_mcp_print_node; in the latter case the data field is used.
Ordinary input files are never deleted. Only temporary JSON files created by this toolset may be cleaned up after reading (and only when dryRun=false).
Very large JSON inputs may be truncated by the MCP transport before the tool reads them. If that happens, insert a smaller blueprint first and add children in follow-up calls with mps_mcp_update_node (ADD/CHILD or SET/CHILD), or pass the JSON as a file path instead of an inline string. See references/staged-construction.md for the recommended pattern.

Reference Index

Open references/json-format.md when you need the unified JSON blueprint shape — concept/properties/children/references layout, optional-section rules, and reference-resolution semantics (r:... vs name auto-resolution).
Open references/staged-construction.md when the subtree is large (>~4 KB) or its child refs are needed for later edits — the skeleton → validate → incremental-fill → targeted-update → cleanup pattern.
Open references/troubleshooting.md when an insert call fails with JsonElement.getAsString() errors or when the JSON shape diverges from the user's textual notation.