Silly Tavern character card fields (5/5): Extensions & debugging — system_prompt, post_history_instructions, extensions

Series: Silly Tavern character card fields (5 parts). These V2 fields aim to align end-user experience with author intent; whether they override global ST settings by default—and whether you can override them in UI—follows the spec’s intent and your ST options. Source: V2 explainer.

system_prompt

Role: system prompt text carried by the card. The spec proposes that, when non-empty, it should replace the user’s global system prompt by default (empty string → fall back to global/default). That reduces drift from users’ global presets.

Example (placeholder—tune for your model):

Reply in English. Play {{char}} talking with {{user}}; avoid repeating the previous sentence verbatim; if unsure, ask one clarifying question before advancing the plot.

Practical check: if changing the global system prompt doesn’t change the character, see whether the card’s system_prompt is non-empty.

post_history_instructions

Role: instructions placed after chat history. The spec notes these often weigh heavily on current models; in some ecosystems this slot parallels concepts like UJB or Jailbreak naming in Silly. When non-empty, it should replace the user’s global post-history slot by default (empty → fall back).

Example:

Keep one voice and one set of names; don’t introduce organizations or places not implied by the card unless {{user}} explicitly adds them.

Keep this short and sharp—it’s a strong lever.

extensions

Role: an object for app-specific data not in the spec; default {}. Importers must not strip unknown keys. Namespacing (e.g. per-app prefixes) reduces collisions—see examples in the upstream repo.

Example (structural only):

{
  "my_tool": {
    "palette": "sepia"
  }
}

Field cheat sheet

Key	What it roughly does
name	Character name; feeds
description	Description; usually in prompt
personality	Personality blurb
scenario	Situation / background
first_mes	First assistant message
mes_example	<START>-separated samples
creator_notes	Human notes; not in prompts
alternate_greetings	Extra greetings array
character_book	Embedded lorebook
tags / creator / character_version	Sorting, attribution, version
system_prompt / post_history_instructions	High-leverage instruction slots (behavior per spec)
extensions	App-specific bag

V1 cards without spec expose the classic six-string root; V2 nests under data.

Debugging (verbs)

1. Detect V1 vs V2 (spec present or not).
2. Hunt conflicts between globals (system / Jailbreak) and card system_prompt / post_history_instructions.
3. Change one thing → re-import → new chat (avoid stale context).
4. Validate JSON (quotes, commas—JSON has no comments).
5. Back up the PNG before surgery.

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