How to Scaffold a Nix flake.nix from a Package List
Nix flakes invent overlays. Lock nixpkgs or write UNKNOWN. Packages only from the list.
The matching generator is the Nix flake.nix from a Package List (No Invented Overlays) prompt. Browse related cards in the PromptDig library (Browse more prompts). When a filled run survives, share the version you actually use (Share a prompt).
Lock nixpkgs input or write UNKNOWN
Scaffold flake.nix (inputs, devShell, packages) from a package list. Do not invent overlays, nixpkgs pins, or unlisted packages. Start by filling Inputs, not by asking the model to remember last week's run. If a field is blank, write NONE or NOT IN INPUTS and leave it blank through Generate. The card is built so the model cannot honestly invent a number, owner, URL, or command that you did not paste.
Paste these fields before you hit run:
Package list for devShell and/or packages: [Packages]
nixpkgs input I lock (URL or UNKNOWN): [Nixpkgs]
System I allow (or UNKNOWN): [System]
Overlay names I allow (or NONE): [Overlays]
Words I must not use: [Banned]
What I must never invent: [Never]
Output format: [Format]
Language for comments: [Lang]
Flake description string I allow: [Desc]
Extra inputs I may name (or NONE): [ExtraInputs]
That inventory is the honesty ledger. Anything that does not appear there is forbidden in the draft. If you catch yourself adding a nice-to-have after the run, you are no longer using the card. You are ghostwriting. Put the extra fact in Inputs and run again.
List only named packages in the shell
Generate is numbered on purpose. Do not skip a step because the first paragraph looked done. The early steps exist to stop later prose from smuggling claims.
Walk the Generate list in order:
- Honesty ledger: Packages, Nixpkgs, System, Overlays, ExtraInputs, Desc, Lang. Forbidden: inventing overlays, inventing pins.
- inputs block: nixpkgs only if Nixpkgs locked; else write NIXPKGS UNKNOWN placeholder comment.
- outputs stub: forEachSystem or single System. If System UNKNOWN, write SYSTEM UNKNOWN.
- devShell: buildInputs/packages only from Packages.
- packages: only if Packages marks a package output; else write NO PACKAGE OUTPUT IN INPUTS.
- overlays: only Overlays; if NONE, do not add overlay =.
- Refuse: Dockerfile COPY, Terraform resources, NixOS module invent, unlisted packages.
- Compliance pass: quote Banned and Never. Gaps list of five. Format as Format.
If a step asks for a version lock, quote the version from Inputs in the output. If a step asks for a refuse list, keep the refuse list in the published artifact, not in a sidebar you delete. Reviewers should see what the model was not allowed to do.
Leave overlays NONE when blank
Most failures are the same shape: a missing field gets a confident fill. A conversion rate appears. A Gradle task appears. A flash point appears. A caption appears on a job that asked for slide text only. Your review is to search the draft for numbers, names, and commands, then grep Inputs. No match means cut.
Honor the constraints as hard stops, not vibes:
- flake.nix from Packages only. Not Dockerfile and not NixOS module.
- Never invent overlays or nixpkgs pins when UNKNOWN/NONE.
- Only packages named in Inputs.
- No emojis.
When the card says not legal advice, not certification, not an exam dump, or not a caption engine, that sentence belongs at the top of the output. Deleting it to look more finished is how you inherit risk.
Refuse Dockerfile and NixOS module padding
Finish with the compliance pass the prompt already asks for. Quote the banned-word hits. Cut them. Print character counts when the job has a cap. Print word counts when the job has a budget. List gaps as gaps. Five missing facts are more useful than one smooth paragraph.
Tags on the card (nix flake from packages, flake.nix scaffold, no invented nix overlays) are a reminder of the job shape, not an invitation to wander into a neighboring cluster. If you need a different surface, open a different PromptDig card rather than stretching this one.
Fill the card, then run
Replace every bracket. Run on ChatGPT, Claude, or Gemini. Read the ledger first, then the artifact. If the model invents a commit, KPI, DOI, PEL, bid, or logo, discard the run. Tighten Inputs. Run again. Share the filled card that survived, not the first draft that sounded done.