modify-structures

The second step of a CAD workflow for editing STEP files, a common format for 3D solid models. It adds specified holes, pockets, vents, mounts, and other details to already-created base parts.

In plain words
What is it for?
It applies manifest-defined cuts and additions to base STEP files, including fastener holes, electronics pockets, camera mounts, vents, and weight-relief features.
Why use it?
It lets you change manufacturing or mounting details without rebuilding the main structural geometry.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/ppak10/rocketsmith/modify-structures
Any agent
npx skills add ppak10/RocketSmith --skill modify-structures
Clone the repo
git clone --depth 1 https://github.com/ppak10/RocketSmith

Made for: Claude Code, Codex.

Per session 57 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,698 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00057 $0.03698
Opus 5 $0.00028 $0.01849
Sonnet 5 $0.00011 $0.00740
Haiku 4.5 $0.00006 $0.00370

Measured 2d ago against content hash aa2d367fe3e8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

modify-structures 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 2d 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.

skills/modify-structures/SKILL.md · 270 lines

How it starts

The opening of the file, as written. The whole thing — 270 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Modify Structures

Overview

modify-structures is Pass 2 of the CAD pipeline. It takes the base STEP files produced by generate-structures and applies detail features specified in each part's modifications list: radial holes for fasteners, through-holes for screws, rectangular pockets for electronics bays, cylindrical pockets for camera mounts, vent holes, weight-relief cuts, and any other subtractive or additive detail operations that aren't part of the structural shell.

The split exists because:

  • Iteration speed — changing hole positions or adding a camera mount doesn't require regenerating the structural shell
  • Review boundaries — you verified the base geometry in Pass 1; Pass 2 is purely "apply these details"
  • Future-proofing — rail buttons, altimeter bay cutouts, payload mounts, and custom user requests all plug into the same modification framework

This skill is rocketry-agnostic — it knows about build123d boolean operations and modification recipes, not about rockets. The manifest's modifications list drives what gets applied.

Core principle: Modifications are applied to base STEPs produced by Pass 1. Do not re-generate base geometry here. If a modification requires changing the structural shell, update the manifest's features block and re-run Pass 1.

Never edit component_tree.json directly to add or change modifications. The modifications list is populated by manufacturing_annotate_tree based on DFAM rules and user-specified overrides. If the modifications list is missing entries the user wants (e.g., rail button holes, vent holes), re-run manufacturing_annotate_tree with the appropriate parameters — do not hand-edit the JSON.

When to Use

  • generate-structures has completed Pass 1 successfully
  • At least one entry in manifest["parts"] has a non-empty modifications list
  • The user asks to add retention hardware, accessory mounts, vent holes, or other detail features

If every part's modifications list is empty (which is the default for a freshly generated DFAM manifest — retention defaults to "none"), skip this skill entirely.

Read the full file on GitHub · 270 lines

Changes

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.

  1. 2d ago First seen · 270 lines · 57 tokens per session scan A aa2d367fe3e8

Subscribe to this mod's changes

modify-structures is a skill published in the GitHub repository ppak10/RocketSmith (21 stars, last pushed 4mo ago), licensed MIT. It adds 57 tokens to every session and 3,698 once invoked, about $0.0003 per session on Opus 5. 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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