Claude Code Runs the Real Ponytail. Cursor and 11 Others Settle for 2,593 Bytes.

Last Updated on August 19, 2026 by Editorial Team Author(s): Chew Loong Nian – AI ENGINEER Originally published on Towards AI. Claude Code Runs the Real Ponytail. Cursor and 11 Others Settle for 2,593 Bytes. Ponytail’s own portability doc lists 22 coding agents. I parsed it and counted: only 9 of them get an adapter the agent actually executes. The other 13 get no runnable adapter at all, and twelve of those get nothing but the same rule body — the 2,593-byte AGENTS.md, or a byte-identical copy of it filed under their own name. That is 39% of the real ruleset, missing every one of its five behaviors. The rest of the article explains how the author computed which hosts truly execute Ponytail’s adapters versus merely read a copied rules file, including the Python script used to classify hosts and the resulting 9 EXEC vs 13 TEXT split (with caveats where installs or manifests blur the edges). It then details what Ponytail is in practice—a decision ladder with safety/guard-rail requirements—and why the “text tier” loses major behavioral controls like intensity levels, off switching, persistence, output contracts, and subagent coverage (notably affecting Cursor and others). The a…