mechanism-behavior-discovery

mechanism-behavior-discovery is a skill for Claude Code from zjunlp/Mechanist. It costs 133 tokens per session (1,649 once invoked), scanned A, original, MIT.

A research guide for discovering interesting, repeatable behaviors in language or multimodal models when no specific behavior has been chosen yet. It turns a candidate observation into a testable claim with data, measurements, and a possible internal location.

In plain words
What is it for?
Use it to search for non-obvious model behaviors, design data and metrics to test them, and prepare a validated phenomenon for mechanism research.
Why use it?
It helps researchers move from a vague question about what a model does to a precise behavior that can be tested and later explained. It also filters for findings that are robust and feasible to investigate.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the mechanist plugin — 54 skills, 4 agents shipped together

Good fit Use it to search for non-obvious model behaviors, design data and metrics to test them, and prepare a validated phenomenon for mechanism research.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/zjunlp/mechanist/mechanism-behavior-discovery
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 zjunlp/Mechanist --skill mechanism-behavior-discovery
Clone the repo
git clone --depth 1 https://github.com/zjunlp/Mechanist

Made for: Claude Code.

Or install mechanist, the plugin that ships this one along with the rest of its 54 skills, 4 agents.

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 mechanism-behavior-discovery

README.md
[![agentmods](https://agentmods.dev/badge/skills/zjunlp/mechanist/mechanism-behavior-discovery/github.svg)](https://agentmods.dev/skills/zjunlp/mechanist/mechanism-behavior-discovery)
Your own site
<a href="https://agentmods.dev/skills/zjunlp/mechanist/mechanism-behavior-discovery"><img src="https://agentmods.dev/badge/skills/zjunlp/mechanist/mechanism-behavior-discovery/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 mechanism-behavior-discovery

Your own site · 80×15
<a href="https://agentmods.dev/skills/zjunlp/mechanist/mechanism-behavior-discovery"><img src="https://agentmods.dev/badge/skills/zjunlp/mechanist/mechanism-behavior-discovery.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 133 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,649 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
SkillSpector: 1 finding, up to low

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • low Excessive Agency · line 20
    Skill's behavior or capabilities extend beyond its stated purpose. Scope creep allows an agent to perform actions unrelated to its documented functionality, increasing the attack surface.
    Fix: Limit the skill's scope to its documented purpose. Remove instructions that enable the agent to perform actions outside its stated functionality.
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 $0.00133 $0.01649
Opus 5 $0.00067 $0.00825
Sonnet 5 $0.00027 $0.00330
Haiku 4.5 $0.00013 $0.00165

Measured 10d ago against content hash 20fa694ac289, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

mechanism-behavior-discovery 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/mechanism-behavior-discovery/SKILL.md · 49 lines

How it starts

The opening of the file, as written. The whole thing — 49 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Mechanism — Behavior Discovery

The discovery half of the loop: before you can explain why a model does something, you need a behavior worth explaining. This skill helps surface a new behavioral phenomenon — a candidate claim — and choose the data that tests it. The sharpened phenomenon (a one-sentence falsifiable behavior, its data/metric, and a plausible internal locus) hands off to /mechanism-explore.

A phenomenon is an observable, reproducible regularity in a model's input→output behavior that is not obvious a priori. A candidate is worth pursuing when it is real, non-obvious, specific, robust, and tractable (a plausible internal locus exists to explain it).

When to Use

The task is open-ended — "find something interesting about how this model behaves," "what's surprising here." Do not use it to explain an already-named behavior (that is /mechanism-explore) or to score a model on a fixed benchmark.

This skill runs only when the phenomenon is not already pinned by the user. When the user explicitly names the phenomenon to investigate, the caller skips discovery entirely and goes straight to explaining that named phenomenon — so a behavior-level override is handled by the caller, not here.

Strategies for Choosing a Behavior to Investigate

  1. Transfer a behavioral phenomenon into a high-stakes domain. Take a behavior already known elsewhere, move it into an important domain, and test whether it reappears — either under the same conditions or under stricter, more counterintuitive ones. Domains include but are not limited to:
    • Science domains: chemistry, biology, medicine, …
    • Language: how language systems evolve and develop, etymological / cognate relationships, ancient-text decipherment, and the language–intelligence relationship.
    • Multi-agent social science.
    • Creativity.
  2. Borrow from the human sciences.
    • Take a finding from brain science, psychology, or developmental history and check whether LLMs exhibit the same behavior.
    • Compare how the human brain and LLMs process the same task, identifying similarities and differences. This usually requires EEG (or other neural) recordings of humans performing that task.
  3. Cross-modal transfer. Take a phenomenon seen in text and check whether it appears in image / video / multimodal models.
  4. Reuse existing results in computer science. Check whether earlier findings, methods, or conclusions in computer science apply to the current model or research question.
  5. Probe a phenomenon's conditions or causal origin. Take a known (or just-surfaced) phenomenon and ask when it holds or why it arises.
    • When it holds — characterize the regime of validity. Macro: under what general condition or law does the phenomenon hold or break? Micro: vary a concrete knob — model scale, checkpoint, prompt format, language, in-context examples, difficulty, or domain — and find the specific point at which the behavior flips. Either a general boundary or a single flipping condition is itself a candidate claim.
    • Why it arises — trace it to a training cause (data frequency, order of acquisition across checkpoints, objective, RLHF stage) or an inference cause (decoding, attention/representation locus, prompt position, context length), yielding a claim of the form "P is caused by C at stage S".
  6. Meta-analysis. Distill a theory or law from prior research — e.g. the scaling law and the Densing Law of LLMs — and use a macro-level or mathematical-theory lens to characterize the regularity, including the conditions under which a given phenomenon holds.

Read the full file on GitHub · 49 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 · 49 lines · 133 tokens per session scan A 20fa694ac289

Subscribe to this mod's changes

mechanism-behavior-discovery is a skill published in the GitHub repository zjunlp/Mechanist (74 stars, last pushed 14d ago), licensed MIT. It adds 133 tokens to every session and 1,649 once invoked, about $0.0007 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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