Build an editor-native skill

This guide builds a skill that takes the selected code, rewrites it from a short instruction, and shows the result as a diff you can review and apply — all launched from the editor, no typing in chat. It uses the two editor-native fields, from: and output.to; for the model behind them, see Editor-native skills.

What we’re building

A rewrite-selection skill that:

reads the selection and the file’s language from the editor,
asks you (once) how to rewrite it,
sends it to the model, and
opens the rewrite as a diff against your selection — nothing changes until you click Apply.

1. The manifest

Create .skiller/skills/rewrite-selection/skill.yaml:

id: rewrite-selection
name: Rewrite Selection
description: Rewrite the selected code from an instruction and show it as a reviewable diff.
version: "1.0.0"

inputs:
  # Filled from the editor at launch. No prompt — if nothing is selected, the
  # input is empty and the skill falls back to asking, so it still works from chat.
  - name: code
    type: string
    from: selection
    description: The selected code

  - name: language
    type: string
    from: activeFile.language
    description: The file's language id

  # A normal prompted input — context never fills this, so you're always asked.
  - name: instruction
    type: string
    required: true
    prompt: "How should I rewrite the selection? (e.g. \"add doc comments\", \"simplify\")"

steps:
  - id: rewrite
    type: llm
    description: Rewrite the selection
    file: steps/01-rewrite.md
    output: rewritten

# Deliver the rewrite as a diff scoped to the launch selection — review, then Apply.
output:
  summary: "{{ outputs.rewritten }}"
  to: diff

The code and language inputs carry from:; instruction doesn’t, so it’s always prompted. That mix is the point — bind what the editor can supply, ask for the rest.

2. The prompt

Create .skiller/skills/rewrite-selection/steps/01-rewrite.md. It’s hardened to emit only the rewritten code (no prose, no fences) so it diffs cleanly:

You are a precise code editor. Rewrite the snippet below according to the instruction.

Language: {{ inputs.language }}
Instruction: {{ inputs.instruction }}

Snippet:
{{ inputs.code }}

Output rules:
- Output ONLY the rewritten snippet. No explanation, no markdown, no code fences.
- Preserve surrounding indentation so it drops back into place.
- Change only what the instruction asks for.

Run @skiller /reload so the registry picks up the new skill.

3. Launch it from the editor

Open any source file and select the code you want to rewrite.
Launch the skill — either:
- right-click → Run Skill → Rewrite Selection, or
- open the Command Palette → Skiller: Run Skill → Rewrite Selection.
Chat opens with the run ready (prefilled by default — see runSurface). Skiller already captured your selection and the file’s language, so it only asks the one thing it can’t read: your instruction.
Answer the prompt. The skill runs and opens a diff of your selection vs. the rewrite.
Review it. Click Apply to accept, or just close it to discard.

Because the result goes to the diff sink, nothing touches your file until you Apply — and if you edited the file while the diff was open, Skiller refuses the stale apply rather than garbling it.

4. Variations

Apply directly instead of reviewing. Swap to: diff for to: editor.replaceSelection to write the rewrite straight back over the selection. It still won’t clobber: if the document changed since launch, the result opens in a new tab instead.
Send a command to the terminal. to: terminal types a drafted command onto your prompt and waits for you to press Enter; to: terminal.run types and runs it. Pair terminal.run with a confirmation step so the command is reviewed before it executes — the bundled shell-it skill does exactly this: drafts a command, confirms it in chat, then runs it.
Save to a file. to: "file:notes/{{ inputs.name }}.md" writes a (templated) workspace file.
It still works from chat. Run @skiller /skill rewrite-selection with no selection and the from: inputs fall back to prompting — the same skill, no editor required.