Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add pzfreo/build123d-mcp --skill b123d-modelinggit clone --depth 1 https://github.com/pzfreo/build123d-mcpWrote 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.
[](https://agentmods.dev/skills/pzfreo/build123d-mcp/b123d-modeling)<a href="https://agentmods.dev/skills/pzfreo/build123d-mcp/b123d-modeling"><img src="https://agentmods.dev/badge/skills/pzfreo/build123d-mcp/b123d-modeling/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/pzfreo/build123d-mcp/b123d-modeling"><img src="https://agentmods.dev/badge/skills/pzfreo/build123d-mcp/b123d-modeling.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00000 | $0.06858 |
| Opus 5 | $0.00000 | $0.03429 |
| Sonnet 5 | $0.00000 | $0.01372 |
| Haiku 4.5 | $0.00000 | $0.00686 |
Grade A, and why
b123d-modeling 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 7d 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.
How it starts
The opening of the file, as written. The whole thing — 489 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Build 3D Geometry with build123d
Use this skill when asked to model, build, or modify a 3D part or assembly with build123d — from a text description, a technical drawing (image or PDF), dimensions in a spec, or an existing STEP/STL file.
Use the build123d-mcp MCP server as the execution and verification authority.
Build incrementally with execute() by default and checkpoint the first valid
model. If matching-view evidence then shows a body-family/global-form mismatch,
keep the replacement in one canonical model.py and run it with execute_file();
then use measure() → validate() → render_view() before exporting it.
execute_file() runs in a clean namespace and preserves the previous valid model
if the rebuild fails, so a necessary global correction does not sacrifice the
verified checkpoint. Do not globally rebuild a checkpoint merely because a
canonical source file is available.
Step 0 — Start the session
reset(), thenexecute("from build123d import *").- Read the
build123d://quickrefresource before writing build code — it has accurate API syntax for the current build123d version. - If the part uses fasteners, bearings, or threads, read
build123d://bd_warehouseand probe catalogue sizes before scripting.
Step 1 — Extract the spec before modeling
Do not model while reading the input. First convert it into a parameter block.
From a technical drawing (image or PDF):
- Identify the views — front / plan (top) / side — and the projection convention; the title block states first- or third-angle, the SCALE (e.g. 2:1), and the units/tolerance standard.
- Printed dimension callouts are real part dimensions. Never replace one with a pixel-derived value, and never multiply a printed dimension by drawing scale.
- Hidden (dashed) lines are internal features — holes, pockets, bores. Centrelines (long-short chain) mark hole centres and symmetry axes. Section hatching shows solid material in a cut view.
- Symbols: Ø diameter (not radius), R radius, M6/M8… threads,
⌴ counterbore, ⌵ countersink, typical hole note
4× Ø6.6 THRU. - Cross-check every feature in at least two views before trusting it — a circle in plan with no matching hidden lines in front is probably a boss, not a hole.
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.
- 7d ago Changed · +39 lines 60ee72b0e0ab
- 11d ago First seen · 450 lines · 0 tokens per session scan A 79749e74e222
b123d-modeling is a skill published in the GitHub repository pzfreo/build123d-mcp (85 stars, last pushed 7d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 6,858 tokens. 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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