Consider GCF as an alternative to TOON for AI-generated feed data

[blackwell-systems]

I noticed Folo uses @toon-format/toon to decode AI-generated feed selection data in the onboarding and new-user-guide flows. There's a data integrity issue worth knowing about, plus a format alternative that may work better for this use case.

TOON crashes on RSS feed titles

TOON's decoder misparses string values containing bracket-colon patterns as inline array headers. RSS feed titles commonly use this pattern:

[Breaking]: Fed raises rates by 0.25%
[Update]: iOS 20 beta 3 released  
[Alert]: Earthquake M6.2 in Japan
[Podcast]: The AI Daily Brief - Episode 247

When the LLM generates individual feed objects with these titles, TOON's decoder crashes:

TOON DECODE ERROR: "[Breaking]: Fed raises rates by 0.25%"
  Invalid array length: "Breaking" (expected non-negative integer with no leading zeros)

Tested on 15 realistic feed records: 14 of 15 crash TOON's decoder. Only the one feed without brackets in the title survives. GCF: zero failures.

Your current code handles this because the LLM produces TOON's tabular format (arrays of objects) which quotes values. But if the model ever returns a single feed object or a differently shaped response, the decoder will crash. This is a latent bug.

TOON corruption details: GCF vs TOON

LLM generation reliability

Your flow depends on the LLM producing valid decoder-parseable output. Across 28 generation runs:

Model	GCF validity	TOON validity	JSON validity
Claude Opus 4.6	5/5	0/5	5/5
Claude Sonnet 4.6	5/5	2-3/5	5/5
GPT-5.5	4-5/5	1-2/5	5/5
Gemini 2.5 Pro	5/5	1/5	5/5

TOON's official decoder rejects LLM-generated output on 7 of 9 models. GCF is producible by every frontier model.

Full generation data: GCF benchmarks

Token savings on feed data

Dataset	JSON	TOON	GCF	TOON vs JSON	GCF vs JSON
15 feeds	521	382	373	26.7%	28.4%
100 feeds	3,472	2,502	2,408	27.9%	30.6%

Data integrity

GCF is verified lossless across 43 billion+ round-trips in 5 formats and 6 languages. Zero failures.

Drop-in replacement

// Before
import { decode } from "@toon-format/toon"
const feeds = decode(output) as FeedToSelect[]

// After  
import { decodeGeneric } from "@blackwell-systems/gcf"
const feeds = decodeGeneric(output) as FeedToSelect[]

Zero runtime dependencies. MIT licensed. TypeScript SDK: npm install @blackwell-systems/gcf

Adoption

Used by OmniRoute (6.1K stars), NetClaw (556 stars), and others.

• Docs: https://gcformat.com
• Benchmarks: https://gcformat.com/guide/benchmarks
• Lossless verification: https://gcformat.com/guide/lossless-verification