qelectrotech-source-mirror/misc/qet-mcp/README.md

qet-mcp — a Model Context Protocol server for QElectroTech projects

A small stdio MCP server that lets an AI assistant read and verify QElectroTech projects: what is in a project, what an edit actually changed, and what a whole corpus of projects contains.

It has no third-party dependencies — Python 3.9+ and the standard library only. The MCP SDK is not required.

Why

Verifying a change by screenshot is unreliable, and this tool exists because that unreliability produced two wrong conclusions in one review session:

• A drag of a multi-element selection looked like it had left the symbols behind and detached their labels. Diffing the saved file showed all four elements had moved by an identical (0, -80) and no label had moved at all. A bug report was one step away from being filed.
• An "Apply" button looked like it did nothing. It was disabled, because a required field was empty.

Both times the pixels misled and the model told the truth. So the tools here read the model.

Tools

Tool	What it answers
qet_project_info	title, format version, folios, element and conductor counts
qet_elements	placed elements: uuid, type, position, label, information bag
qet_conductors	conductors and their documentation fields; filter by attribute
qet_diff	what an edit actually changed — element moves, adds, removes, relabels; conductor changes; and folio fields, texts, shapes, images, symbol text fields and terminal strips
qet_scan	sweep a directory of projects, counting nodes carrying an attribute
qet_element_info	a .elmt: translated names, terminals, info fields, part counts
qet_export	run a headless export (pdf, png, svg, bom, cables, wires, wiring, nets, links, info)
qet_edit	change a project — place, move, rotate, label, wire, number, cross-reference, add text, shapes and images, restyle a symbol's text fields, delete; then diff the result
qet_element_build	author a .elmt — draw a new symbol, with terminals to wire it by
qet_project_new	start from nothing — an empty project with a title and folios
qet_element_search	find a symbol in a collection by name (any language), type or terminal count
qet_check	design-rule checks — duplicate labels, unlabelled masters, unnumbered conductors, empty folios
qet_query	ask the project database — read-only SQL over the views and tables

qet_export and qet_edit launch QElectroTech. Everything else parses the file directly, which is faster, needs no display, and cannot be confused by a dialog.

Running it

# list the tools and exit
misc/qet-mcp/qet_mcp.py --list

# speak MCP on stdin/stdout
misc/qet-mcp/qet_mcp.py

Register it with an MCP client, for example:

{
  "mcpServers": {
    "qet": {
      "command": "python3",
      "args": ["/path/to/qelectrotech/misc/qet-mcp/qet_mcp.py"],
      "env": {
        "QET_MCP_WORKSPACE": "/home/you/drawings",
        "QET_ENABLE_SCRIPTING": "1"
      }
    }
  }
}

Five tools need scripting switched on

A QElectroTech with JavaScript scripting switched off refuses --run, and off is the default from #984 onwards. Five tools here drive it that way and stop working until it is turned on:

need QET_ENABLE_SCRIPTING=1	qet_query, qet_continuity, qet_check, qet_project_new, qet_edit
unaffected	everything else — they read the .qet directly, or, in qet_export's case, use a plain CLI flag

The variable goes in the environment this server is started in, which for an MCP client is the env block above; the server passes its environment straight through to QElectroTech. It does not set the variable itself, on purpose — a switch a program turns on for itself is not a switch. Whoever configured this server and pointed it at a QElectroTech binary made that choice, and their interactive QElectroTech keeps whatever its own setting says.

Without it, those five come back "ok": false with a hint naming the variable. Older builds, from before the setting existed, need nothing.

What the server is allowed to touch

Every path in a tool call is chosen by the model, so without a policy this server would be a read/write primitive for anything the operating system lets the process reach: read any project on the disk, export one somewhere else, overwrite an unrelated file, embed an arbitrary local image or PDF.

So data paths are confined to a workspace:

QET_MCP_WORKSPACE	the directories tool calls may read and write, separated by : (; on Windows)
unset	the directory the server was started in
QET_MCP_ALLOW_ANY_PATH=1	turns the check off entirely

Set the workspace to the folder your drawings live in. A path outside it is refused with an error naming what was allowed; symlinks are resolved first, so a link planted inside the workspace is judged by where it points.

Two arguments are deliberately not confined: binary (the qelectrotech executable) and elements_dir (the element collection). Those are configuration, chosen once by whoever runs the server, and both normally live in /usr or a build tree — outside any sensible workspace. Confining them would reject the ordinary case while stopping nothing.

QET_MCP_ALLOW_ANY_PATH=1 is equivalent to granting the client local filesystem access with this process's privileges. It exists so that is a deliberate choice rather than the default.

Nothing is overwritten unasked. qet_export, qet_edit, qet_project_new and qet_element_build refuse an output that already exists unless the call passes "overwrite": true. Replacing a file is the one step this server cannot undo, so it is the one step it will not take on its own.

The confinement is applied where tool arguments enter the server, not inside each tool. Importing qet_mcp and calling tool_export() from your own Python is not confined and is not meant to be — that is your code calling a library, and you already chose the paths.

Worked examples

What did that edit change?

{"name": "qet_diff", "arguments": {"before": "a.qet", "after": "b.qet"}}

"elements": { "moved_count": 4,
              "distinct_move_deltas": [[0.0, -80.0]],
              "relabelled": [], "info_changed": [] }

Four elements moved by one uniform delta; nothing was relabelled. That is the answer a screenshot gave wrongly.

Draw something, and check it landed

{"name": "qet_edit", "arguments": {
  "binary": "/path/to/qelectrotech",
  "project": "in.qet", "output": "out.qet",
  "elements_dir": "/path/to/qelectrotech/elements",
  "operations": [
    {"op": "add_folio", "id": "f"},
    {"op": "set_folio_title", "folio": "$f", "title": "Starter"},
    {"op": "add_element", "id": "k1", "folio": "$f", "path": "common://.../coil.elmt", "x": 100, "y": 100},
    {"op": "add_element", "id": "k2", "folio": "$f", "path": "common://.../coil.elmt", "x": 320, "y": 100},
    {"op": "add_conductor", "folio": "$f", "from": "$k1", "from_terminal": 0, "to": "$k2", "to_terminal": 0},
    {"op": "set_conductor", "folio": "$f", "element": "$k1", "terminal": 0, "property": "num", "value": "W7"},
    {"op": "set_label", "folio": "$f", "element": "$k1", "label": "KM1"}
  ]}}

An op that creates something takes an "id"; later ops name it as "$id". Terminals are addressed by index — top to bottom, then left to right, not the order the .elmt lists them. qet_element_info and qet_element_search both report that index order. The answer carries a per-operation result and a qet_diff, because "addConductor → true" says the call was accepted, not that the file came out right:

"diff": {"elements":   {"before": 11, "after": 13, "added": ["{0aa3…}", "{6f63…}"]},
         "conductors": {"before": 47, "after": 48, "added": ["4:{0aa3…}/{2904…}--{6f63…}/{2904…}"],
                        "removed": []}}

Draw a symbol that does not exist yet

{"name": "qet_element_build", "arguments": {
  "output": "/path/to/collection/99_custom/my_resistor.elmt",
  "names": {"en": "Test resistor", "fr": "Résistance de test"},
  "parts": [
    {"type": "rect", "x": -10, "y": -20, "width": 20, "height": 40},
    {"type": "line", "x1": 0, "y1": -30, "x2": 0, "y2": -20},
    {"type": "line", "x1": 0, "y1": 20,  "x2": 0, "y2": 30},
    {"type": "text", "x": 14, "y": -4, "text": "R"}
  ],
  "terminals": [{"x": 0, "y": -30, "orientation": "n", "name": "1"},
                {"x": 0, "y": 30,  "orientation": "s", "name": "2"}]}}

Then place it with qet_edit like any catalogue element. Unlike a project, a .elmt is not rewritten by QElectroTech on a round trip, so generating one here is safe in a way that generating a .qet would not be — there is no toXml() waiting to drop what this writer did not know to emit.

Ask a question the XML cannot answer

{"name": "qet_query", "arguments": {
  "binary": "/path/to/qelectrotech", "project": "industrial.qet",
  "sql": "SELECT label, COUNT(*) AS n FROM element_nomenclature_view WHERE label <> '' GROUP BY label HAVING n > 1 ORDER BY n DESC"}}

"rows": [{"label": "V6", "n": 7}, {"label": "V5", "n": 6}, {"label": "V4", "n": 6}]

Duplicate element labels in a shipped example — a design-rule question, answered by the database that already knew it.

How much of a corpus uses a field?

{"name": "qet_scan",
 "arguments": {"directory": "examples", "tag": "conductor", "attribute": "cable"}}

{ "files": 24, "total": 3190, "non_empty": 0, "distinct_values": [] }

Across the shipped examples: 3190 conductors, not one with a cable value.

Testing

python3 test_qet_mcp.py                      # unit + protocol, no QElectroTech needed
QET_BINARY=/path/to/qelectrotech \
QET_ELEMENTS=/path/to/qelectrotech/elements \
QET_EXAMPLES=/path/to/qelectrotech/examples \
QET_ENABLE_SCRIPTING=1 \
    python3 test_qet_mcp.py                  # everything

QET_ENABLE_SCRIPTING=1 matters from #984 onwards: without it the integration tests that drive QElectroTech through a script all fail, and they fail as "the edit did nothing" rather than as "scripting is off", which reads like a regression in the thing under test.

176 tests in three layers: unit (validation, script generation, the terminal order rule, the diff, the part schema), the real stdio transport, and integration against a built QElectroTech. Several exist because the behaviour they pin was once wrong and looked right, and say so in their docstrings. To check the suite itself rather than trust it, each of those bugs was reintroduced in turn and the suite confirmed to fail: ten in the Python, plus the hang guard on addConductor and the database refresh in ConductorCreator in the C++.

Notes and limits

• The project database is reachable now, through qet_query. It was not when this server was written, which is why every other structural tool here re-derives its answer from the XML. Prefer the views — element_nomenclature_view, project_summary_view, wiring_list_view — which exist to be queried; the underlying tables are how the cache is arranged today and a column may move. Call qet_query with no sql to list both. Only SELECT and WITH are accepted, which is the rule QElectroTech applies to its own custom-query box, not one invented here. An empty result and a failed query are told apart: row_count 0 with no error means nothing matched, and a typo'd column name says so.
• Texts, shapes and images are in the database too, one row each in drawing_item_view (uuid, kind, folio, position and size, and a description: the shape type or the text). The uuid is the one saved in the file, and every qet_edit op that takes a text, shape or image index also takes that uuid, which does not shift the way an index does. qet_element_build gives every part of a symbol a uuid as well, returned in part_uuids; qet_element_info lists them in part_list.
• qet_export isolates its launch. SingleApplication keys its socket on applicationFilePath(), so a second launch of the same binary path forwards its request to an already-running instance and returns that process's answer with no error. The tool copies the binary to a unique temporary path, gives it a private HOME, and runs it on the offscreen platform. A symlink would not work: applicationFilePath() resolves it back to the real path.
• The CLI matches its flags exactly. --export-bom out.csv is the supported form; --export-bom=out.csv is not recognised as an export at all, so the application starts its interface instead and a headless run hangs. The tool uses the positional form.
• Conductor identity is the hard part of qet_diff. A conductor names its ends with terminal1/terminal2, and the project format has two schemes: folio-scoped integer ids in older files, terminal-definition uuids plus element1/element2 in newer ones. The integer ids are renumbered on every save, so keying on them — which this tool did at first — made all 47 conductors of an untouched folio read as removed and re-added the moment the other side had been through QElectroTech, which is exactly what qet_edit produces. They are now keyed by owning element uuid plus terminal, which is stable across a save: measured at 0 colliding keys over 3190 conductors in the 24 shipped examples, and 0 churn on a no-op edit. Where an element predates persisted uuids the end cannot be resolved and keeps a #-marked unstable key; the diff then reports unstable_keys and says so rather than pretending to be comparable.
• Texts, shapes and images are keyed by uuid when every one on both sides has one, so an edit or a move reads as a change to that item. A file saved before they carried a uuid has none; for such a pair (including a legacy file against its first re-save) that kind falls back to position, where an edited text reads as removed plus added and a move as a removal plus an addition. Each section says which it used in keyed_by. The folio version attribute is left out of the comparison on purpose: QElectroTech rewrites it on every save, and including it made every folio of any re-saved project look edited.
• Elements written before persisted uuids fall back to a positional key, which makes a move in such a file read as a remove plus an add.
• qet_edit needs a build whose scripting API carries the drawing verbs. Against an older one it reports exactly which methods are missing and changes nothing. addElement and the move/delete verbs shipped with the scripting API; addConductor, rotateElement, setElementLabel, setElementInfo and setFolioTitle are newer.
• elements_dir is not optional for common:// paths. The sandboxed run has its own empty HOME, so QElectroTech falls back to the compiled-in collection path, which on a machine that never ran make install does not exist. The only symptom is addElement reporting that a file plainly present "does not resolve to an element". An absolute .elmt path works without it.
• set_conductor changes the whole potential, not one segment. That is what the application does — a wire number describes a potential — so name a terminal carrying exactly one conductor and the change reaches every conductor electrically joined to it. A terminal several conductors meet at names none of them and is refused, so address a potential from one of its leaves. Property names are the file's own, so qet_conductors reads back exactly what was set.
• link_elements takes a folio for each end, because a master and its slave are normally on different folios. Whether a pair may be linked is decided by QElectroTech's own isLinkable(), so a script cannot make a link the GUI would refuse.
• An element must live inside a collection to be placeable. This is not about the path syntax: an absolute .elmt path works, but only if the file sits under a directory QElectroTech knows as a collection. Write it under the tree you pass as elements_dir and qet_edit can place it, by absolute path or as common://…; write it anywhere else and add_element reports only "does not resolve to an element".
• qet_element_build computes the .elmt size header, and checks it. width/height/hotspot_x/hotspot_y relate to the drawing by a containment constraint, not a formula — the declared box runs from (-hotspot_x, -hotspot_y) to (width - hotspot_x, height - hotspot_y) and the drawing must fit inside it. The shipped collection shows authors picking their own margins (one element pads 2 units left and 3 right, another 8 and 2), so there is no convention to copy, only an invariant to satisfy. A drawing that escaped its box is the classic way a hand-written element renders clipped in the collection panel while looking fine in XML.
• QElectroTech interrupts a script at 30 s of its own accord, separately from this tool's timeout. A very long operation list will hit that first.
• qet_edit never writes the input. It saves to a separate file and diffs the two, so the original is always the thing the diff is against.