AI Guides › Skills & Agents
The Guardrails Section Is The Most Important Part Of Any Skill You Write
By Nigel Guy · 2 min read
Most people writing their first skill treat the guardrails section — if they
write one at all — as a formality tacked on at the end, the legal disclaimer
of the document. That's backwards. The instructions tell the skill what to
do when everything goes right. The guardrails are the only part that
matters when something doesn't.
The rule: write the guardrails section before you consider the skill
finished, and write it by asking "what's the worst plausible way this gets
misused or goes wrong," not "what should I disclaim."
The mechanism
- List the failure modes you can actually imagine, specifically. Not
"may make mistakes" — "may misread a date format and schedule the wrong
day," or "may summarise a document without flagging that a page was
skipped."
- Name what the skill should never do automatically. Anything
irreversible, anything involving money, anything sent externally without
review — these deserve an explicit "always confirm before" line, not an
assumption that the user will remember to check.
- State what it can't verify. If the skill relies on information that
could be stale or wrong (a schema, a price, a policy), say so plainly
rather than implying confidence the skill doesn't actually have.
- Write one line about scope. What this skill is not for — the
adjacent task someone might reasonably try to use it for, that it wasn't
built to handle.
- Re-read the guardrails section cold, a week later. If it still reads
as obviously true and specific rather than generic, it's done its job.
What to skip
Skip generic guardrails that could paste onto any skill unchanged ("use
responsibly," "verify important information") — they signal that nobody
actually thought about this skill's specific failure modes. And skip writing
the guardrails last, as an afterthought; write them as soon as you can
picture the first way this goes wrong, which is usually before you've
finished the main instructions.
Guardrails
- A skill with vague guardrails is often a skill whose author didn't fully
think through what it does — treat that as a signal when reading someone
else's skill, not just when writing your own.
- The guardrails section should get harder to write, not easier, as the
skill's scope grows. If it's staying short while the skill takes on more
responsibility, that's worth noticing.
- Guardrails written once go stale. Revisit them whenever the skill's scope,
the tools it touches, or the stakes of getting it wrong actually change.
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