Claude Prompt Codes Retested: L99 Sharper, OODA Narrower, ARTIFACTS Faded, and 3 New Codes to Use

Six months ago a Reddit user shared three prompt codes that modify Claude's behavior when placed at the start of a message: L99 for architectural decisions, OODA for time-pressured calls, and ARTIFACTS for multi-output tasks. A retest this week across 6 fresh production tasks reveals which still work, which shifted, and three new codes worth adopting.

Retest Results

• L99 – Sharper than before. The hedge-reducing effect is more pronounced on Sonnet 4.6 and Opus 4.7. Wins decisively for architectural decisions where you want a real opinion, not a list of considerations.
• OODA – Narrows. Still excellent for incident response (forces discipline panicked humans skip), but now fails on open-ended strategic questions. Newer Claude leans harder into OODA structure than substance when there's no real time pressure. Use only when a clock is running.
• ARTIFACTS – Faded. Newer Claude versions structure multi-output responses by default, so the explicit code adds less. Still useful for synthesis tasks (interview transcripts, RFP responses, multi-deliverable scoping) but unnecessary for code-shaped outputs. Usage dropped to ~1/3 of October levels.

Three New Codes for Daily Rotation

• /skeptic – Challenges your framing before answering. Saves you from charging ahead with a wrong premise. Combine with L99 for code reviews.
• /blindspots – Forces Claude to surface what you didn't think to check. Caught a case-sensitive path bug the team had chased for hours.
• /decompose – Breaks fuzzy tasks into testable subtasks ranked by leverage.

Stacking Note

Stacking 3+ codes confuses newer Claude versions. It picks one to honor and partially honors the others. Stick to 2-code stacks. The L99 + /skeptic combination is now the go-to for code reviews.