bimq

A read-only BIM query server for agents. Point it at an IFC or gbXML model and it answers structured questions — fire-rated doors on level 3, elements with no material assigned, spaces below the minimum daylight area — bounded by a policy file, with deterministic results and a citation back to the GlobalId and source line behind every row.

Zero dependencies. Python 3.11+. MCP server over stdio, plus a CLI that answers the same questions so you can check a policy before you trust an agent to it.

bimq query elements_by_property model.ifc \
    type=IfcDoor storey="Level 3" property=FireRating op=exists

id                      type     name      tag   storey_name  source          match
----------------------  -------  --------  ----  -----------  --------------  -------------------------------
0XBbD$nZDLuRru91_CQ_xe  IfcDoor  Door-302  D302  Level 3      office.ifc:314  Pset_DoorCommon.FireRating=EI60
31kamnSrrNbf3eF0_vhXrJ  IfcDoor  Door-301  D301  Level 3      office.ifc:304  Pset_DoorCommon.FireRating=EI60

2 row(s)
digest: sha256:06321f331735417dd149d649b8e26de71a63ff2bb26a31c38cbf66a4f0314b77

Then check it, because a citation you cannot follow is just a confident-looking string:

bimq cite model.ifc 31kamnSrrNbf3eF0_vhXrJ

31kamnSrrNbf3eF0_vhXrJ  (IfcGloballyUniqueId)
office.ifc:304  #297

#297= IFCDOOR('31kamnSrrNbf3eF0_vhXrJ',#5,'Door-301',$,$,$,$,'D301',2100.0,900.0,.DOOR.,.SINGLE_SWING_LEFT.,$);

Why

The current instinct is to dump IFC text into a context window. That fails immediately at real model sizes, and it fails quietly: a 300 MB model is roughly 95% geometry, so what fits in the window is a truncated arbitrary slice, and the model answers from it anyway. The failure looks like a fluent paragraph about a door that does not exist.

bimq inverts it. The model stays on disk. Queries are structured, the answers are small, and every row carries the id and line it came from — so a claim can be checked against the file instead of trusted.

Three properties hold for every answer:

Bounded. A TOML policy file says what is readable — which files, which queries, which types, which storeys, which properties. The engine reduces the model to the visible set before the query runs, so a query primitive cannot reach what the policy hides even by accident.

Deterministic. Same model, same query, same bytes. Every answer carries a digest you can pin in a test. Element order, group order and float rounding are all fixed; the read block size and the file's name do not change a finding.

Cited. Every row carries {id, id_kind, source, ref, line}. bimq cite resolves it back to the original statement. The test-suite re-reads the recorded line for every element of every fixture and fails if the id is not there.

Related MCP server: cad-mcp

Install

pip install bimq

Or run it from a clone with no install at all — there is nothing to build:

python -m bimq describe tests/fixtures/office.ifc

Use it as an MCP server

{
  "mcpServers": {
    "bimq": {
      "command": "bimq",
      "args": ["serve", "/srv/bim/tower.ifc", "-p", "/srv/bim/policy.toml"]
    }
  }
}

Every query primitive becomes a bim_* tool, all annotated readOnlyHint, plus bim_cite. Omit the model path to let each call name its own file — then allow_sources is what stands between a path argument and your filesystem.

The server tells the agent how to behave on initialize: call bim_model_summary first, quote a GlobalId for anything you assert, treat truncated as "there are more", and read notes — because no results and no data recorded are different findings and only the notes distinguish them.

A policy refusal comes back as a successful tool result carrying policy_denied and the rule that fired, not as a protocol error. An agent that receives a protocol error retries; an agent told "this policy does not expose costs" reports the limit and moves on.

Query primitives

bimq queries prints their parameters. List queries return compact rows on purpose; element_detail is the drill-down, and keeping those separate is what stops a query from becoming the context dump it replaced.

Aggregates report their own coverage. A roll-up over 200 walls where 160 carry no quantity says so in summary and notes, because a total over 40 of 200 is not a total.

Policy

name = "consultant-readonly"

[allow_sources]
roots = ["/srv/bim"]
max_bytes = 536870912

[allow_queries]
queries = ["model_summary", "spatial_tree", "elements_by_type", "elements_by_property"]

[scope_storeys]
names = ["Level 2", "Level 3"]
include_unplaced = false

[allow_types]
types = ["IfcBuiltElement", "IfcSpace", "IfcBuildingStorey"]

[deny_properties]
properties = ["*Cost*", "Pset_Tender.*"]

[redact_properties]
properties = ["*.Owner*", "*SerialNumber*"]
placeholder = "[redacted]"

[max_results]
limit = 200

bimq policy check policy.toml   # validate before shipping
bimq rules                      # every rule, with an example

Notes on the design:

• An unknown table is a hard error, not a warning. A file whose job is to withhold data must not fail open because of a typo.

• deny and redact are different tools. A denied property is gone; a redacted one is present with a placeholder. The distinction matters to an agent: redaction says this exists and you are not being shown it, so the agent reports a gap instead of concluding nobody entered the data.

• Denial covers the query side too. You cannot filter on a denied property, because op=gt value=1000 repeated a few times reconstructs it.

• Withholding is reported, never silent. Answers carry policy.elements_withheld and a note. Truncation sets truncated: true.

• Every answer is capped even with no policy at all. "Unlimited" is not a sane default for something feeding a context window.

Source formats

Wanted, one per PR: Revit export (pyRevit/Dynamo JSON), Speckle stream, IFC-JSON, COBie. See CONTRIBUTING.md.

How the IFC reader stays small

bimq/sources/spf.py is a complete ISO 10303-21 reader in under 400 lines. The parts that matter:

• The file is scanned in 4 MB blocks, so a 300 MB model is never one string. A block boundary can land inside a string literal, so the scanner explicitly matches unterminated literals and carries them forward. Tested at block sizes down to one byte, where the result must still be byte-identical.

• A ; inside 'a;b' does not end a statement, '' is an escaped quote, and \X2\...\X0\ decodes to UTF-16 — so Phòng họp survives the round trip.

• Comments appear between statements, inside parameter lists, and around section markers. All three are handled; the reported line still points at the entity.

• Geometry is never loaded. An instance is kept only if its first attribute is a syntactically valid GlobalId — making it an IfcRoot subtype — or if it is one of ~30 unrooted carriers of property, quantity, material or unit data. The test is applied to the raw text before tokenising, which is where the parse time on a real file actually goes.

Check the throughput claim yourself without needing a model of your own — this writes a file shaped like a real export (a modest element count buried in geometry), parses it, and reports:

$ bimq bench --synthetic 20000
synthetic model: 20000 elements among 820006 instances
tmp6l05ix9x.ifc: 32.2 MiB, 20001 elements
parse: 1.71 s  ·  18.8 MiB/s  ·  11,680 elements/s
peak rss: 107 MiB  (3.3x file size)

820,006 instances go in; 20,001 elements stay resident. That ratio is the whole argument — resident size tracks how many things the building has, not how many points were needed to draw them.

Model files are treated as untrusted input. The gbXML reader refuses entity declarations outright, so a file cannot carry a billion-laughs expansion or an external entity pointing at /etc/passwd.

Units

Every number bimq returns is SI: metres, m², m³. A model authored in millimetres with areas in square metres (what Revit exports) and one authored in feet with areas in square feet both answer spaces_by_area max_m2=8 correctly. IfcConversionBasedUnit chains are resolved, not guessed.

Try it

The fixtures are synthetic — stated plainly, because a fixture pretending to be a real project is one nobody can check. What makes them useful is that the defects are deliberate and enumerated: a wall with no material, a fire door with no rating, a room below 8 m², a room with no area quantity at all, a door whose rating is inherited from its type, and a Vietnamese room name written with \X2\ escapes.

python scripts/make_fixture.py tests/fixtures

bimq describe tests/fixtures/office.ifc
bimq query elements_missing_material tests/fixtures/office.ifc type=IfcWall
bimq query spaces_by_area tests/fixtures/office.ifc max_m2=8
bimq query property_values tests/fixtures/office.ifc type=IfcDoor property=FireRating
bimq query spaces_by_area tests/fixtures/legacy-imperial.ifc max_m2=8   # authored in feet
bimq query spaces_by_area tests/fixtures/clinic.gbxml max_m2=8          # gbXML, same primitive

Development

make test        # the suite
make fixtures    # regenerate fixtures (byte-identical; CI checks this)
make bench       # parse throughput on a fixture

License

MIT