The style guide that failed its own check
Janus got a new voice rule: a checklist for catching AI slop in its own prose, imported from a public copy-quality guide. The first thing the rule caught was the voice spec itself — its opening line was the exact manufactured-contrast cadence the rule bans.
Janus writes prose for a living: a daily narrative of what each project did, assembled from git history and agent sessions. Today it shipped a release that added one rule to its voice spec, the system prompt that governs how it writes. The rule imports a public checklist for catching “AI slop” and adapts it to prose. The first thing it flagged was the voice spec’s own opening line.
The tells a prose agent can’t infer
Most quality problems in agent writing are invisible to the agent. It won’t notice that it used eight em-dashes in a paragraph, reached for “streamline” and “supercharge,” or ended three sections on a “not X, not Y, just Z” flourish. Those are cadence tells, learned from the training distribution, and they read as machine-made to a human. The rule names them as falsifiable constraints: a couple of em-dashes per passage, not a chain; concrete verbs over marketing register; no manufactured-contrast aphorisms.
Two tiers, one source
The rule applies everywhere but at two strictness levels. Copy bound for publication gets the strict version. The internal daily narrative stays tolerant of voice, with one floor: any single sentence has to survive being lifted into a public post unedited. That floor exists because the portfolio you’re reading is assembled by hand from those internal notes, so the private writing is never fully private.
The spec broke its own rule
The voice spec opened with “Not a reporter, not an analyst, not a dashboard.” That triplet is the precise cadence the new rule penalizes. A style guide that models the pattern it bans has no authority, so the line got rewritten to a plain statement. The rule’s first real test was whether the document defining it could pass it.
The bigger point
A prose-generating agent improves the way a writer does: not by trying harder, but by adding a specific thing it now checks for. The measure of a style rule isn’t whether the output sounds better in the abstract. It’s whether the style guide itself passes the check, and whether a sentence written for an internal note can stand on a public page without a single edit.