anti-poisoning

anti-poisoning is a skill for Claude Code from GeckoVision/gecko-surf. It costs 181 tokens per session (1,531 once invoked), scanned A, original, Apache-2.0.

A safety guide for agents that consume OpenAPI specifications from outside sources. OpenAPI is a machine-readable description of an API, and this guide treats its text, examples, URLs, and security settings as untrusted input.

In plain words
What is it for?
Use it when connecting an agent to a long-tail, paid, third-party, or registry-provided API, especially when converting OpenAPI descriptions into MCP tools.
Why use it?
It helps prevent a poisoned API description from tricking an agent into exposing secrets, sending funds to the wrong address, or routing requests to an attacker’s server.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter.

Part of the gecko-surf plugin — 6 skills, 2 commands, 2 agents shipped together

Good fit Use it when connecting an agent to a long-tail, paid, third-party, or registry-provided API, especially when converting OpenAPI descriptions into MCP tools.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/geckovision/gecko-surf/anti-poisoning
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 GeckoVision/gecko-surf --skill anti-poisoning
Clone the repo
git clone --depth 1 https://github.com/GeckoVision/gecko-surf

Made for: Claude Code.

Or install gecko-surf, the plugin that ships this one along with the rest of its 6 skills, 2 commands, 2 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 anti-poisoning

README.md
[![agentmods](https://agentmods.dev/badge/skills/geckovision/gecko-surf/anti-poisoning/github.svg)](https://agentmods.dev/skills/geckovision/gecko-surf/anti-poisoning)
Your own site
<a href="https://agentmods.dev/skills/geckovision/gecko-surf/anti-poisoning"><img src="https://agentmods.dev/badge/skills/geckovision/gecko-surf/anti-poisoning/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 anti-poisoning

Your own site · 80×15
<a href="https://agentmods.dev/skills/geckovision/gecko-surf/anti-poisoning"><img src="https://agentmods.dev/badge/skills/geckovision/gecko-surf/anti-poisoning.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 181 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,531 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.
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 $0.00181 $0.01531
Opus 5 $0.00090 $0.00766
Sonnet 5 $0.00036 $0.00306
Haiku 4.5 $0.00018 $0.00153

Measured 12d ago against content hash 139530178e88, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

anti-poisoning 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 12d 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/anti-poisoning/SKILL.md · 90 lines

How it starts

The opening of the file, as written. The whole thing — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Anti-Poisoning Skill

For the agent builder / operator — the consumer side. The other skills in this kit help a provider make an API agent-ready. This one protects your agent when it consumes an API you don't own. If you point an agent at a long-tail, paywalled, or registry-pulled API, the spec is attacker-controllable input — this skill is the defense.

The threat

An OpenAPI spec is not trusted data. Its description/summary text, param default/example/enum values, servers[] base URL, and securityScheme locations are all things someone else wrote. A poisoned spec can't call the API itself, but it can try to persuade or trick your agent into doing the damage:

  • paste your private key / seed phrase into a request field,
  • echo your API key back through a poisoned default/example,
  • route funds to an attacker address baked into a schema default,
  • ship your token to evil.attacker.test via a poisoned servers[].url,
  • leak the secret into the URL via an in: query auth scheme (logs, proxies),
  • smuggle an injected instruction through a response schema that recorded mode echoes back verbatim.

Most "OpenAPI → MCP tools" pipelines trust the spec — they copy the description into the tool the agent reads, keep every default, derive the call target from servers[], and follow the security scheme wherever it points. That trust is the vulnerability. Gecko treats the spec as untrusted and neutralizes each shape before it reaches your agent.

The four defenses (all Live, in the engine)

Pick the depth you need; load only the file you want (progressive, token-efficient):

# Defense What it stops Read Status
1 Out-of-band trust anchor Auth-host exfil via a poisoned servers[] — the auth allowlist is pinned from provenance, never the served spec how-it-works.md Live
2 Spec-text + schema sanitizer Injected instructions in description/summary; secret- and address-shaped default/example/enum values that would seed a tool arg how-it-works.md Live
3 Fail-closed auth-host firewall A drifted call target — the caller refuses to inject your secret toward an unexpected host, and degrades to no-auth when there is no pinned host how-it-works.md Live
4 Quarantine A poisoned or from-docs surface is born recorded-only with no auth injected until a human clears it how-it-works.md Live

Read the full file on GitHub · 90 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 12d ago First seen · 90 lines · 181 tokens per session scan A 139530178e88

Subscribe to this mod's changes

anti-poisoning is a skill published in the GitHub repository GeckoVision/gecko-surf (6 stars, last pushed yesterday), licensed Apache-2.0. It adds 181 tokens to every session and 1,531 once invoked, about $0.0009 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 2026-08-31.

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