Yesterday somebody on r/PromptEngineering shipped the tool every spec-writer secretly needed: a terminal app that interviews YOU about the gaps in your own project brief before a coding agent finds them the hard way.
u/trashcoder writes detailed seed prompts before handing anything to a coding agent, and still watches the agent guess its way through decisions that only ever existed in trashcoder’s head. So they built specfill, a CLI that reads your spec, researches the topic, then asks you one question at a time about the architecture calls, edge cases, and UI choices you forgot to write down.
Here’s the twist. Specfill doesn’t rewrite your document. It merges your answers back into the original spec, keeps the structure and tone intact, lets new answers overwrite contradictions, and leaves anything you skip marked unresolved instead of inventing an answer for you. That last part is the whole trick: most tools fill silence with a guess, this one leaves silence as silence.
How to run it:
- 📝 Write your seed prompt like you normally would
- 💻 Run
uvx specfillin your project folder - 🎤 Answer the interview one question at a time (one run reportedly took 20+ minutes and still surfaced major decisions)
- 📄 Get back a merged spec you can commit to the repo as your actual design record
- 🤖 Hand that spec to your coding agent, gaps closed
Pro tip: This isn’t Plan Mode. Plan Mode gives you a plan for right now. Specfill gives you a document that outlives the session, so the next agent, or the next you, inherits the decisions instead of re-litigating them.
Tools of the day: Specfill supports OpenAI, Anthropic, Google, and OpenAI-compatible providers, with GPT-5.6 Sol recommended via API or a ChatGPT/Codex subscription.
Grab it here: github.com/kklemon/specfill. If your specs keep getting reinterpreted by the agent, this is your fix.
I built a TUI that interviews you on missing gaps in your project prompts
by u/trashcoder in PromptEngineering