Find the right kind of error

Symptom	Meaning and next step
Python or check.py not found	Install Python 3.11+, extract the ZIP, and run commands from its top folder. See Lesson 1.
JSON parse error / duplicate key	Use double quotes, remove trailing commas/comments and keep one value per field. The checker does not silently take the last duplicate.
Structural error at a JSON path	Compare that field’s type, required parent and constraints in the matching schema version. 1.0 is not accepted as an integer by this checker.
Bundled schema hash mismatch	Download a fresh complete bundle. Do not edit the schema to make a broken pack pass.
Structure passes; host rejects	Inspect the semantic report: unknown IDs, invalid state paths, contradictory scopes or stale paragraph digests require host checks.
content_review_required / unreviewed material	Complete the actual source/content review. Do not set accepted merely to bypass it.
missing_asset / invalid_attachment	Attach every declared file; compare bytes, size, MIME and SHA-256. Local paths alone do not upload media.
Invalid avatar/sprite	Check a square pixel crop, matching canvas dimensions, transparency and decoded frame budget. See artwork and animation.
Animation unknown in a 0.5 pack	Compare exact schema digests and reader support. Protocol version alone cannot identify a schema revision.
Playground submit rejects 0.3–0.5	Its uploader is 0.2-only. Use an authorized compatible host workflow; the docs checker is structural only.
Context selector unavailable	This is a service configuration issue for the host maintainer, not a missing story sentence. Local offline checks do not require that service.
Correct state test, poor prose	Deterministic rules do not guarantee model interpretation or writing quality. Record a private trial, revise the observation/instructions and replay it.

Keep a minimal failing pack, the exact schema SHA, the command or host/client version and the actual error. Remove credentials and private source material before sharing a report. The final lesson provides a repeatable trial checklist.