How do I install the Prepare Build skill?

Run npx skillmds@latest add https-deeplearning-ai/prepare-build in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Prepare Build safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Prepare Build?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Prepare Build free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Prepare Build?

https-deeplearning-ai (@https-deeplearning-ai) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Prepare Build by https-deeplearning-ai

Name: Prepare Build
Author: https-deeplearning-ai

Prepare Build

Prepares a new build run for a course in the spec-build-lab — allocates the run folders, snapshots the spec into a frozen eval copy and a working copy, drops a session breadcrumb, and moves into the build folder. Does NOT do the building itself; that's the user + agent's subsequent work in builds/run-NN/. Use this skill ANY time the user signals intent to begin building an app from spec.md — including phrasings like "prepare a build", "set up a build", "start a new build", "begin the build", "kick off the build", "kick off run-02", "let's build the app", "let's build it", "build the X app from the spec", "implement the spec", "I'm ready, let's build", "let's do another build", "/prepare-build", or simply launching into coding work inside a course folder that has a spec.md. INVOKE PROACTIVELY — treat any clear build intent as the trigger. Do NOT use this skill to run an existing build, build a docker image, or build features in unrelated projects.

File contents

prepare-build

Allocate the next run-NN, snapshot the spec, drop a session breadcrumb that /extract-build-log will use later, and move into the build folder. Does NOT start the build — building is the agent's subsequent work.

Steps

Verify cwd is a course folder. Confirm all exist relative to cwd: spec.md, builds/, evals/, materials/. If any are missing, refuse with: "Run /prepare-build from inside a course folder — cd courses/<name> first." Stop.

Allocate the next run number.

highest=$(ls -1 builds/ 2>/dev/null | grep -E '^run-[0-9]+$' \
  | sed 's/run-//' | sort -n | tail -1)
next=$(printf "run-%02d" $(( ${highest:-0} + 1 )))

Create the run dirs and snapshot the spec.
```
mkdir -p "builds/$next" "evals/$next"
cp spec.md "evals/$next/spec.md"   # frozen snapshot, read by /eval-spec-vs-build
cp spec.md "builds/$next/spec.md"  # working copy, read by the build agent
```
The eval snapshot at evals/$next/spec.md is judged against later by /eval-spec-vs-build, so the run is judged against the spec it was actually built from even if spec.md is regenerated. The working copy at builds/$next/spec.md makes the build folder self-sufficient — the agent reads ./spec.md from inside the build folder and has no reason to navigate back up to the course folder, where materials/ sits and is forbidden.
Drop the session breadcrumb. Write the absolute path of the current Claude Code transcript JSONL to evals/$next/.session. The path is built from $CLAUDE_PROJECT_DIR and $CLAUDE_CODE_SESSION_ID:
```
slug=$(echo "$CLAUDE_PROJECT_DIR" | sed 's:/:-:g')
transcript="$HOME/.claude/projects/$slug/$CLAUDE_CODE_SESSION_ID.jsonl"
echo "$transcript" > "evals/$next/.session"
```
If $CLAUDE_CODE_SESSION_ID is unset for any reason, fall back to the most recently modified *.jsonl in $HOME/.claude/projects/$slug/ and write that path. The file is per-run, write-once at allocation, never updated.
Announce. Say verbatim, replacing NN: "Run NN — building in builds/run-NN/. Read spec.md (in this folder) and nothing else from the parent course folder. When the build is in a state worth capturing, run /extract-build-log run-NN to slice the conversation into evals/run-NN/session-log.md."
Move into the build folder. cd builds/$next. From here on the agent develops the app inside this folder.

Notes

The breadcrumb at evals/run-NN/.session is a label on the run-NN folder, not coordination state. It's never updated and never read by any other tool — only /extract-build-log consumes it, and only when the user explicitly asks for an extract. Nothing recorder-like is running in the background.
The whole conversation is already being persisted by Claude Code into ~/.claude/projects/<slug>/<session>.jsonl; the breadcrumb just remembers which transcript to slice.

Don't

Don't generate or modify spec.md here — that's /generate-spec.
Don't ask the user for a run number — allocation is automatic.
Don't reuse an existing run-NN folder. Every new build is a new run, even with the same spec.md, so runs and their evals can be compared.
Don't read ../materials/, ../../materials/, or any course materials during the build. The build is a function of spec.md only — that's what the eval pipeline assumes. A PreToolUse hook blocks materials access from inside a build folder; if the hook is bypassed for any reason, /extract-build-log surfaces a contamination warning.

---name: prepare-builddescription: Prepares a new build run for a course in the spec-build-lab — allocates the run folders, snapshots the spec into a frozen eval copy and a working copy, drops a session breadcrumb, and moves into the build folder. Does NOT do the building itself; that's the user + agent's subsequent work in builds/run-NN/. Use this skill ANY time the user signals intent to begin building an app from spec.md — including phrasings like "prepare a build", "set up a build", "start a new build", "begin the build", "kick off the build", "kick off run-02", "let's build the app", "let's build it", "build the X app from the spec", "implement the spec", "I'm ready, let's build", "let's do another build", "/prepare-build", or simply launching into coding work inside a course folder that has a spec.md. INVOKE PROACTIVELY — treat any clear build intent as the trigger. Do NOT use this skill to run an existing build, build a docker image, or build features in unrelated projects.---# prepare-buildAllocate the next `run-NN`, snapshot the spec, drop a session breadcrumbthat `/extract-build-log` will use later, and move into the build folder.Does NOT start the build — building is the agent's subsequent work.## Steps1. **Verify cwd is a course folder.** Confirm all exist relative to cwd: `spec.md`, `builds/`, `evals/`, `materials/`. If any are missing, refuse with: "Run /prepare-build from inside a course folder — `cd courses/<name>` first." Stop.2. **Allocate the next run number.** ```bash highest=$(ls -1 builds/ 2>/dev/null | grep -E '^run-[0-9]+$' \ | sed 's/run-//' | sort -n | tail -1) next=$(printf "run-%02d" $(( ${highest:-0} + 1 ))) ```3. **Create the run dirs and snapshot the spec.** ```bash mkdir -p "builds/$next" "evals/$next" cp spec.md "evals/$next/spec.md" # frozen snapshot, read by /eval-spec-vs-build cp spec.md "builds/$next/spec.md" # working copy, read by the build agent ``` The eval snapshot at `evals/$next/spec.md` is judged against later by `/eval-spec-vs-build`, so the run is judged against the spec it was actually built from even if `spec.md` is regenerated. The working copy at `builds/$next/spec.md` makes the build folder self-sufficient — the agent reads `./spec.md` from inside the build folder and has no reason to navigate back up to the course folder, where `materials/` sits and is forbidden.4. **Drop the session breadcrumb.** Write the absolute path of the current Claude Code transcript JSONL to `evals/$next/.session`. The path is built from `$CLAUDE_PROJECT_DIR` and `$CLAUDE_CODE_SESSION_ID`: ```bash slug=$(echo "$CLAUDE_PROJECT_DIR" | sed 's:/:-:g') transcript="$HOME/.claude/projects/$slug/$CLAUDE_CODE_SESSION_ID.jsonl" echo "$transcript" > "evals/$next/.session" ``` If `$CLAUDE_CODE_SESSION_ID` is unset for any reason, fall back to the most recently modified `*.jsonl` in `$HOME/.claude/projects/$slug/` and write that path. The file is per-run, write-once at allocation, never updated.5. **Announce.** Say verbatim, replacing NN: "Run NN — building in builds/run-NN/. Read `spec.md` (in this folder) and nothing else from the parent course folder. When the build is in a state worth capturing, run `/extract-build-log run-NN` to slice the conversation into evals/run-NN/session-log.md."6. **Move into the build folder.** `cd builds/$next`. From here on the agent develops the app inside this folder.## Notes- The breadcrumb at `evals/run-NN/.session` is a label on the run-NN folder, not coordination state. It's never updated and never read by any other tool — only `/extract-build-log` consumes it, and only when the user explicitly asks for an extract. Nothing recorder-like is running in the background.- The whole conversation is already being persisted by Claude Code into `~/.claude/projects/<slug>/<session>.jsonl`; the breadcrumb just remembers which transcript to slice.## Don't- Don't generate or modify `spec.md` here — that's `/generate-spec`.- Don't ask the user for a run number — allocation is automatic.- Don't reuse an existing run-NN folder. Every new build is a new run, even with the same `spec.md`, so runs and their evals can be compared.- Don't read `../materials/`, `../../materials/`, or any course materials during the build. The build is a function of `spec.md` only — that's what the eval pipeline assumes. A `PreToolUse` hook blocks materials access from inside a build folder; if the hook is bypassed for any reason, `/extract-build-log` surfaces a contamination warning.

Frequently asked questions