A guide to HTTP Parameter Pollution, where an attacker sends repeated or conflicting values for the same web request parameter. It covers testing both server-side and browser-side handling.

Testing how web servers, applications, and client-side code process duplicate parameters during security reviews.

It helps reveal cases where different parts of an application interpret repeated parameters differently.

hpp — Skill for Claude Code by mohdhaji87/payloadsallthethings-skills

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 mohdhaji87/payloadsallthethings-skills --skill hpp

Clone the repo

git clone --depth 1 https://github.com/mohdhaji87/payloadsallthethings-skills

Made for: Claude Code.

Or install payloadsallthethings, the plugin that ships this one along with the rest of its 61 skills.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/mohdhaji87/payloadsallthethings-skills/hpp/github.svg)](https://agentmods.dev/skills/mohdhaji87/payloadsallthethings-skills/hpp)

Your own site

<a href="https://agentmods.dev/skills/mohdhaji87/payloadsallthethings-skills/hpp"><img src="https://agentmods.dev/badge/skills/mohdhaji87/payloadsallthethings-skills/hpp/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/mohdhaji87/payloadsallthethings-skills/hpp"><img src="https://agentmods.dev/badge/skills/mohdhaji87/payloadsallthethings-skills/hpp.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 19 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,706 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.

Origin unknown 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.

Model	Per session	Once invoked
Fable 5.1	$0.00019	$0.01706
Opus 5.5	$0.00008	$0.00682
Sonnet 5.5	$0.00004	$0.00341
Haiku 4.5	$0.00002	$0.00171

Measured 2mo ago against content hash 9e75303d82e7, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

hpp scanned grade A with 1 finding 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 2mo 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl "https://target.com/page?id=1&id=2"

payloadsallthethings/skills/hpp/SKILL.md · 285 lines

The source is not reproduced here

A licence we could not identify

The repository carries a LICENSE file, but it is custom or dual enough that GitHub cannot name it and neither can this catalogue. Unknown terms are not permission, so the body is not copied here. Read the licence at the source and decide for yourself.

Read it on GitHub

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.

2mo ago First seen · 285 lines · 19 tokens per session scan A 9e75303d82e7

Subscribe to this mod's changes

hpp is a skill published in the GitHub repository mohdhaji87/payloadsallthethings-skills (21 stars, last pushed 10mo ago), with no licence file. It adds 19 tokens to every session and 1,706 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.