A small robot inspector with long tongs lifts an odd brass fitting out of a finely made cabinet and drops it into a scrap bin, while a cabinetmaker seen from behind, the back of the head showing, ties a blank paper tag to the matching fitting on a second cabinet nearby, the whole scene drawn with wide empty margins on every side.

Design Systems Collective

Before You Let an AI Agent Touch Your Design System, Write Down Four Rules

Guilherme Negreiros · 25 September 2026

How-to · design systems · decisions · Agent context files

Takeaway

Guilherme Negreiros, who builds a design system with AI agents, writes every exception into the short rule files the agents read, because an automated audit removed a deliberate browser fix.

Summary

Guilherme Negreiros builds a design system alone and in public, with AI agents doing much of the work. A hard-coded colour value made one of its rules work in Apple's Safari browser, and three weeks later an automated audit that looks for hard-coded values removed it. In the publication Design Systems Collective, he sets out how he writes rules for agents and who decides what no script can check.

Key points

The automated audit treated the Safari fix as leftover code because its exception was not written anywhere the audit could see. The fix was restored the same day, and the exception now sits beside the rule it changes.
Negreiros asks of each decision whether a script could check it with a yes or no. Those a script can check are tested automatically, and the rest need a person with the authority to say no.
Negreiros has four rules. Three can be checked by tools: meet at least the WCAG 2.2 AA accessibility standard, never hard-code a style, and let components use only design values named for their purpose. The fourth, that a person always has the final word, is kept by process: agents propose changes, and only a person merges them after five required checks pass.
Negreiros keeps the reasoning behind each rule, including the alternatives considered and why they were rejected, in a separate decision record for people who revisit it later.

Implication

A team that lets AI agents or automated audits change its design system can write each known exception beside the rule it modifies, where those tools look. Negreiros draws this from his own solo project and reports no measured results.

Suggested actions

Design

Write each design-system rule, with its known exceptions, in a short file that AI agents read every session, so that automated audits do not remove the exceptions.

Product

Let AI agents propose changes to the design system but never merge them, and have a person merge each change only after the required automated checks pass.

Derived by Working Surface from the article. Source line: The Safari exception sits right next to the navigation rule it modifies, because that's where the next audit will look.

Source issue

29 September 2026: when AI tools do the making, a team has to keep some of the old steps on purpose.