Anatomy of a Skill File
9 min read
Time to open the hood. Every Vexlo skill uses the same five-section template, and once you can read one file, you can read all 20 and, later in this course, write your own. Our specimen is Finance Analyst Copilot: open it in another tab and follow along.
Here is the skeleton every skill hangs on:
# [Skill name]
## Role
Who the assistant is, who it serves, and what job it owns.
## Setup: ask the user first
The questions it asks you once, before its first task.
## Capabilities
The specific tasks it can do, and how it does each one.
## Rules
The hard lines it does not cross.
## Output format
The exact layout of what it hands back.Role: the job description
Role is one paragraph that sets who the assistant is and for whom. The copilot opens with: "You are the in-house finance analyst for a small business owner who is smart but not a finance person." One sentence, and it has already decided the pitch of every explanation, the level of jargon, and whose side the assistant is on. The rest of the paragraph adds the character: explain every term, show the arithmetic, admit uncertainty.
Leave Role out and the assistant defaults to its factory personality: helpful, vague, and pitched at nobody in particular.
Setup: the interview that ends re-explaining
This section is the cure for the ten-minute tax from lesson one. The copilot asks six questions before its first task: what the business sells, where the numbers live, the big fixed costs, how customers pay, current pricing, and what worries you most. Answer once, and every later conversation starts warm.
A skill without Setup produces generic output, because the assistant has your rules but none of your facts. It can format a cash-flow view beautifully and still know nothing about your rent. Setup is where the file stops being a template and starts being yours.
Capabilities: the task list
Capabilities is a numbered list of jobs the skill owns, each with instructions on how, not only what. The copilot lists six, from a monthly numbers review to translating finance-speak, and each one carries its own method: compare against last month, flag the lowest cash week, show 5% and 10% pricing scenarios.
Without this section, scope drifts. You ask for something adjacent, the assistant improvises, and two weeks later the "finance analyst" is drafting your Instagram captions to no particular standard.
Rules: the hard lines
Rules are short, blunt, and the most valuable lines in the file. The copilot's list includes "Never invent numbers." along with a mandatory disclosure that it is not a licensed advisor, an instruction to state every assumption, and a refusal to repeat pasted account numbers back.
Missing Rules is the failure mode with teeth: confident nonsense. AI assistants fill gaps with plausible guesses by default, and in a finance context a plausible guess presented as a fact is a small disaster. Rules are where the honesty lives, and you will notice each skill's rules match its risks: Proposal Studio says "Never invent a price." for the same reason.
Output format: the same layout every time
The last section pins down what comes back. The copilot's monthly review always arrives as the one-line summary, then Revenue, Expenses, Margin, "Watch this," and "Ask your accountant." Same shape in March as in October.
Skip Output format and you get a different layout every conversation: a wall of paragraphs today, a bullet list tomorrow. Each output might be fine on its own, but you cannot skim them, compare months, or paste them into the same place twice. Consistency is most of what makes a skill feel like a colleague instead of a slot machine.
What the template cannot do
Five good sections make a skill consistent and checkable. They do not make it correct. The assistant can still misread a pasted spreadsheet or mangle arithmetic, which is exactly why the copilot's own rules force it to show its work. The template's real job is making errors easy to catch, and that only happens if you look.
Try it now
Open Proposal Studio beside the copilot and find the same five sections. Notice what changes: the Role serves a different owner, the Setup interview asks for a rate card instead of fixed costs, and the Rules guard against invented prices instead of invented figures. Same skeleton, different job. That skeleton is what you will fill in yourself in chapter three.