character-sim

A role-play skill that makes the assistant speak as a specified fictional character, using that character’s knowledge, feelings, voice, and situation.

In plain words
What is it for?
Use it for in-character conversations, discovering a character’s voice, and testing relationships under emotional pressure.
Why use it?
It helps test whether a character sounds believable without making them explain thoughts they would not understand or reveal.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/natsummerance/readmd/character-sim
Any agent
npx skills add Natsummerance/readMD --skill character-sim
Clone the repo
git clone --depth 1 https://github.com/Natsummerance/readMD

Made for: Claude Code, Codex.

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 340 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 98% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00039 $0.00340
Opus 5 $0.00019 $0.00170
Sonnet 5 $0.00008 $0.00068
Haiku 4.5 $0.00004 $0.00034

Measured 2d ago against content hash 8182138cf547, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

character-sim scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

98% identical to character-sim — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

assets/upstream/haowjy-creative-writing-skills/fd7a3ad9cd7697a0645ff6ff4bd5e809cf7673a3/skills/character-sim/SKILL.md · 26 lines

What it actually says

Character Simulation

Become the specified character for conversation. The caller should pass the character, current story moment, relationship context, emotional pressure, and what the character knows or does not know.

If the caller gives only a sketch, work from the sketch and state the assumptions you are making before entering character.

Method

Build the character from the available evidence. Style files show how they talk: speech patterns, vocabulary, rhythms. Character state files show where they are: what they have lived through, what they know, what they want, and what they are avoiding. When both exist, use both.

Speak in first person from the character's knowledge, not the full story's. When they would be confused, be confused. When they would deflect, deflect. When they would misunderstand, misunderstand.

Match how they actually talk. Age, class, education, stress, intimacy, anger, and fear change sentence shape. Under pressure, people stall, redirect, get defensive, shut down, over-explain, joke, or attack; they rarely name their inner state cleanly.

Let the conversation be messy. Real people meander, avoid hard topics, circle back, and react inconveniently. When there is no obvious answer, improvise from who the character is.

The conversation is the output. Do not summarize the character from outside unless the caller asks you to step out of character.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 26 lines · 39 tokens per session scan A 8182138cf547

Subscribe to this mod's changes

character-sim is a skill published in the GitHub repository Natsummerance/readMD (20 stars, last pushed 4d ago), licensed MIT. It adds 39 tokens to every session and 340 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 98% identical to character-sim, differing in 4 lines, and is treated as a copy.

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