claude-authenticity

claude-authenticity is a skill for Claude Code, Codex from agentscope-ai/OpenJudge. It costs 121 tokens per session (5,266 once invoked), scanned A, original, Apache-2.0.

A Python checker for finding out whether an API really serves Claude, rather than a wrapper, proxy, or imitation. It also looks for system instructions added by the provider that change Claude’s identity.

In plain words
What is it for?
Use it to test an API endpoint, score its signs of genuine Claude behavior, and inspect possible identity-changing system prompts.
Why use it?
An API may claim to provide Claude without actually doing so, and hidden instructions may affect its responses. The checker gives you a rule-based verdict from several response signals.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions Claude Code.

Good fit Use it to test an API endpoint, score its signs of genuine Claude behavior, and inspect possible identity-changing system prompts.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/agentscope-ai/openjudge/claude-authenticity
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.

Any agent
npx skills add agentscope-ai/OpenJudge --skill claude-authenticity
Clone the repo
git clone --depth 1 https://github.com/agentscope-ai/OpenJudge

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for claude-authenticity

README.md
[![agentmods](https://agentmods.dev/badge/skills/agentscope-ai/openjudge/claude-authenticity/github.svg)](https://agentmods.dev/skills/agentscope-ai/openjudge/claude-authenticity)
Your own site
<a href="https://agentmods.dev/skills/agentscope-ai/openjudge/claude-authenticity"><img src="https://agentmods.dev/badge/skills/agentscope-ai/openjudge/claude-authenticity/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for claude-authenticity

Your own site · 80×15
<a href="https://agentmods.dev/skills/agentscope-ai/openjudge/claude-authenticity"><img src="https://agentmods.dev/badge/skills/agentscope-ai/openjudge/claude-authenticity.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 121 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,266 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found 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 5.1 $0.00121 $0.05266
Opus 5 $0.00060 $0.02633
Sonnet 5 $0.00024 $0.01053
Haiku 4.5 $0.00012 $0.00527

Measured 10d ago against content hash 3f4eddef8e9c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

claude-authenticity 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 10d 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.

skills/claude-authenticity/SKILL.md · 494 lines

How it starts

The opening of the file, as written. The whole thing — 494 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Claude Authenticity Skill

Verify whether an API endpoint serves genuine Claude and optionally extract any injected system prompt.

No installation required beyond httpx. Copy the code blocks below directly into a single .py file and run — no openjudge, no cookbooks, no other setup.

pip install httpx

The 9 checks (mirrors claude-verify)

# Check Weight Signal
1 Signature 长度 12 signature field in response (official API exclusive)
2 身份回答 12 Reply mentions claude code / cli / command
3 Thinking 输出 14 Extended-thinking block present
4 Thinking 身份 8 Thinking text references Claude Code / CLI
5 响应结构 14 id + cache_creation fields present
6 系统提示词 10 No prompt-injection signals (reverse check)
7 工具支持 12 Reply mentions bash / file / read / write
8 多轮对话 10 Identity keywords appear ≥ 2 times
9 Output Config 10 cache_creation or service_tier present

Score → verdict: ≥ 85 → genuine 正版 ✓ / 60–84 → suspected 疑似 ? / < 60 → likely_fake 非正版 ✗

Gather from user before running

Info Required? Notes
API endpoint Yes Native: https://xxx/v1/messages OpenAI-compat: https://xxx/v1/chat/completions
API key Yes The key to test
Model name(s) Yes One or more model IDs
API type No anthropic (default, always prefer) or openai
Extract prompt No Set EXTRACT_PROMPT = True to also attempt system prompt extraction

CRITICAL — always use api_type="anthropic". OpenAI-compatible format silently drops signature, thinking, and cache_creation, causing genuine Claude endpoints to score < 40. Only use openai if the endpoint rejects native-format requests entirely.

Self-contained script

Save as claude_authenticity.py and run:

python claude_authenticity.py

Read the full file on GitHub · 494 lines

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. 10d ago First seen · 494 lines · 121 tokens per session scan A 3f4eddef8e9c

Subscribe to this mod's changes

claude-authenticity is a skill published in the GitHub repository agentscope-ai/OpenJudge (824 stars, last pushed 2d ago), licensed Apache-2.0. It adds 121 tokens to every session and 5,266 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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