Design review

The checks answer "will it print and will it fit". The design review comes after them: is the part a good design for its purpose and for the style you chose? The AI looks at the numbers from design_metrics and at renders, then suggests concrete changes. It never changes the part without your OK.

The rules it applies, with their sources, are on Design styles and review (IDs DS-*).

Styles

Style	For	What the review pushes
functional (default)	brackets, mounts, jigs	visible faces oriented well, no supports on show faces, a corner for the seam, one or two screw sizes
modern	things on a desk or a wall	one radius language (an edge-break size and at most one styling radius), ≥ 90 % of edges rounded or chamfered, symmetry where the function allows, screws out of sight
least_cost	spares, prototypes, many copies	less support, pocketed bulk, several copies when a small part is all layer time
rugged	outdoors, in a car, dropped	ASA (or PETG in shade) instead of PLA, no water traps, rounded corners, inserts and stainless screws
soft	held in the hand	rounded edges, grips 30-40 mm across, no gently domed tops that show layer steps

The industrial look (chamfers and exposed standard screws) is functional with EDGES = "chamfer". You can also write your own styles.

Pick one per part, in the script's Dims:

@dataclass(frozen=True)
class Dims:
    ...
    STYLE: str = "rugged"  # typed by the user

A variant can change it (VARIANTS = {"desk": dict(STYLE="modern")}). Without STYLE, the workspace's style setting applies, else functional. For a new part the AI asks once if you have said nothing about looks.

Optional, for a more precise review (Dims or module level, print orientation):

• SHOW = ["+Y", "+Z"]: the sides seen in use. Layer-step and support findings are limited to them. Without it the AI asks, when it matters, or judges every face.
• UP = "+Y": the side that points up in use, for the water-trap check.
• EDGES = "chamfer" or "fillet": the edge language the part should keep to.

Custom styles

A style is a small TOML file, the same kind as the built-in ones. Put yours in ~/.config/b123d-print/styles/<name>.toml (for all your workspaces) or in styles/<name>.toml next to the workspace's b123d-print.toml (for one project). The first one found wins: workspace, then yours, then built-in, so a file with a built-in's name replaces it. based_on starts from another style: every field the file sets replaces the inherited one (per field, including review, which is replaced, not appended), and false switches an inherited threshold off.

# ~/.config/b123d-print/styles/soft_modern.toml
label = "Soft modern"
description = "Modern, with 2 mm fillets everywhere and no visible screws."
based_on = "modern"
edges = "fillet"
min_treated_edge_share = 1.0   # every outside edge rounded
max_edge_break_sizes = 0       # no small edge breaks...
max_styling_radii = 1          # ...one radius: the 2 mm one
max_chamfer_sizes = false      # inherited from modern: switched off (bed chamfers are fine)
review = """
Look for: 2 mm fillets on every outside edge and nothing else; no screw heads on any visible
side (use SHOW); the rest as in modern [DS-G1, DS-G3].
Typical: "the 1 mm and 3 mm fillets become 2 mm".
"""

Use it like a built-in: STYLE = "soft_modern".

b123d-print styles lists every style and where it comes from; b123d-print styles soft_modern shows one with based_on applied. Over MCP, list_parts lists them. A field the file does not know, a wrong type, a missing based_on style or a loop is an error that says which file and which field.

Field	Type	What it does
label	text	the name shown in reports
description	text	one line: what the style is for
based_on	text	another style this one starts from
edges	"chamfer", "fillet" or ""	the edge language for parts that set no EDGES
review	text	what the reviewer looks for; printed at the end of design_metrics and used as the style's rubric
max_shallow_slope_share	number	suggest when more of the up-facing (or SHOW) area than this is tilted 1-30° from flat (layer steps; DS-S1)
supports_on_visible	true/false	suggest when supports sit under a visible side (SHOW with -Z; DS-S2)
seam_note	true/false	note when no contour corner can take the seam (DS-S3)
max_screw_sizes	whole number	suggest when more distinct screw sizes than this appear (DS-G3)
min_treated_edge_share	number	suggest when less of the outside edge length than this is rounded or chamfered (DS-G1)
max_edge_break_sizes	whole number	suggest when more distinct radii up to 1 mm than this appear (DS-G1)
max_styling_radii	whole number	suggest when more distinct radii over 1 mm than this appear (DS-G1)
max_chamfer_sizes	whole number	suggest when more distinct chamfer sizes than this appear (DS-G1)
max_sharp_edge_share	number	suggest when more of the outside edge length than this is sharp (DS-G8, DS-R7)
min_symmetry	number	note when the best mirror symmetry is below this (DS-G7)
hidden_screws_note	true/false	note to keep screw heads off the SHOW sides (DS-G3)
max_support_share	number	suggest when supports weigh more than this share of the part (DS-C4)
max_infill_share	number	suggest pocketing when infill is more than this share of the filament (DS-C5)
max_layer_time_share	number	suggest printing several when per-layer time is more than this share (DS-C7)
outdoor_material	true/false	suggest ASA or PETG when the material is PLA or not set (DS-R1)
max_water_cm3	number	suggest a drain when the part holds more water than this with UP up (DS-R3)
curved_supports_note	true/false	note that organic supports scar curved faces less (DS-H2)

Shares are fractions (0.9 = 90 %). The built-in files are in src/b123d_print/data/styles/: copy one as a starting point.

Running it

From an MCP client, use the design_review prompt (or ask for a design review): it runs check, then design_metrics, renders the part and reports 3-7 suggestions, each with its rule ID, the change in numbers, its effect and its trade-off. Then it asks which ones to apply.

From the command line:

b123d-print metrics bracket --style modern

bracket
style: modern (argument), up: +Z
assumes 2 walls, 15% infill, 0.2 mm layers, 5/3 top/bottom, density 1.24 (material not set: PLA assumed), print_flow 10 mm3/s

part: 60.0 x 30.0 x 40.0 mm, 11.4 cm3
  filament 8.2 g, shell 87% / infill 13%  [simple estimate, roughly ±20 %]
  time ~21 min  [rough estimate: extruded / 10 mm3/s + 200 layers x 3 s]
  supports 0.0 g on 0 face(s)
  edges: sharp 100%, filleted 0%, chamfered 0% of 400.0 mm; radii -, chamfers -; bed edges sharp 180 mm
  stepping: 0.0 cm2 up-facing shallow slopes (0%, all faces)
  symmetry: x 0.616, y 1.0; seam corners on 100% of layers; water traps 0 cm3 (+Z up)

economy: 1 part(s), 10 faces, screw sizes {'M3': 2}

findings:
  [SUGGEST] DS-G1 part: 0% of outside edges are rounded or chamfered (target >= 90 %, bed edges excluded)

--json gives every number. metrics never fails: the review only suggests.

The numbers

Metric	How
size	bounding box, volume, area, aspect ratios (reported only: no proportion rule)
filament, cost	shell (2 walls, 5 top / 3 bottom layers) plus 15 % infill, times the material's density; cost when filament_price is set. A simple estimate, roughly ±20 %
time	extruded volume / print_flow + layers × 3 s. A rough estimate; print_flow (default 10 mm³/s) is the one setting that adjusts it
supports	faces steeper than the overhang limit that are not short bridges, times their height above what is below them, about 20 % solid. Rough
stepping	the area tilted 1-30° from flat, where layer steps show (vertical walls and flat tops are clean)
edges	outside edges: sharp, filleted, chamfered shares; the distinct radii and chamfer sizes; bed edges apart
symmetry	overlap of the part with its mirror image about the x and y mid-planes
economy	parts, faces; round holes matched to likely screw sizes (a guess)
seam corners	share of layers whose outline has a sharp corner where the seam can hide
water traps	water left in the part with UP up (voxel grid, drains sideways and down)

Use the estimates to compare two versions of a part and to see what dominates (supports, infill, layer count), not as a quote: a slicer gives the real numbers.

Settings

style, filament_price and print_flow in the settings; density in the material profiles. The printer profile's nozzle and layer height are used when a printer is set.