# Independent Review: Codex (OpenAI)

**Date:** 2026-06-11
**Model:** Codex (fresh session, local SPEC.md)
**Specs reviewed:** RFC 8259 (JSON), TOON v3.3, GCF v2.0 (local checkout with all fixes)
**Verdict:** Picks GCF generic if forced to choose non-JSON replacement
**Note:** Previous Codex run reviewed v1.4 (cached raw URL) and ranked GCF last. With v2.0, Codex flipped to GCF.

## Rankings

| Category | Winner |
|----------|--------|
| Cleanest arbitrary nesting | JSON |
| Best compact nested records | **GCF** |
| JSON round-trip fidelity | JSON, **GCF** close behind |
| Graph at scale (500+) | **GCF** ("by a huge margin") |
| Spec rigor (challengers) | **GCF** |
| Agent replacement pick | **GCF** (conditional) |

## Key quotes

> "If forced to select a non-JSON replacement, I would choose GCF generic."

> "GCF wins because real tool responses are rarely perfectly flat."

> "For graph-heavy payloads, it is not close: GCF provides structural information TOON simply does not model."

> "GCF is more rigorous than TOON on paper."

> "TOON is a competent compact table format surrounded by an increasingly awkward attempt to become a general notation."

> "GCF's best generic feature is the attachment mechanism."

> "The - versus ~ distinction correctly preserves explicit null versus an absent property."

> "These are semantic compression, not merely punctuation removal." (on graph profile)

## v1.4 → v2.0 flip

Previous review (v1.4) ranked GCF last on round-trip fidelity, last on nested data, and chose TOON over GCF. With v2.0:
- Round-trip: GCF "effectively tied" with JSON, TOON "clearly behind"
- Nested data: GCF "most cleanly among compact formats"
- Spec rigor: GCF "more rigorous than TOON on paper"
- Replacement pick: flipped from TOON to GCF

Every v1.4 criticism was addressed by v2.0.

## GCF criticisms (v2.0)

- Two formats sharing punctuation (generic + graph)
- Graph profile is fixed five-field code-symbol schema, not general property graphs
- Canonical number "enough digits" doesn't define a unique algorithm
- Strict-only hostile to LLM-authored output
- "Stable" is a project lifecycle declaration
- Truncated root object may still parse (counts only protect counted containers)

## TOON criticisms

- "Optional key folding is the worst design. Same bytes decode into different JSON structures."
- -0 becomes 0, out-of-domain numbers may approximate or stringify
- "Configurable normalization, not a dependable round trip"
- Forbidding trailing newline, empty root as empty document
- No wire-level version marker
- Requires counts before arrays, obstructing real streaming
- "Its compact table is a fast path, not a general solution"

## Full verdict

"TOON is a competent compact table format surrounded by an increasingly awkward attempt to become a general notation. GCF is more complex and less mature, but its complexity buys capabilities that matter in agent pipelines."
