harden

harden is a skill for Claude Code from HK-hub/AgentSkills. It costs 62 tokens per session (2,189 once invoked), scanned A, a copy of harden, MIT.

An interface-hardening guide for handling errors, unusual input, long text, translations, and other real-world edge cases.

In plain words
What is it for?
Use it to improve error states, text overflow, internationalization, validation, network failures, permissions, and large or empty data sets.
Why use it?
It helps prevent interfaces from breaking when data is missing, text is longer than expected, services fail, or users work in different languages.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter. Also seen: positional $N argument.

Good fit Use it to improve error states, text overflow, internationalization, validation, network failures, permissions, and large or empty data sets.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/hk-hub/agentskills/harden
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 HK-hub/AgentSkills --skill harden
Clone the repo
git clone --depth 1 https://github.com/HK-hub/AgentSkills

Made for: Claude Code.

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 harden

README.md
[![agentmods](https://agentmods.dev/badge/skills/hk-hub/agentskills/harden/github.svg)](https://agentmods.dev/skills/hk-hub/agentskills/harden)
Your own site
<a href="https://agentmods.dev/skills/hk-hub/agentskills/harden"><img src="https://agentmods.dev/badge/skills/hk-hub/agentskills/harden/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 harden

Your own site · 80×15
<a href="https://agentmods.dev/skills/hk-hub/agentskills/harden"><img src="https://agentmods.dev/badge/skills/hk-hub/agentskills/harden.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 62 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,189 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 94% 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 5.1 $0.00062 $0.02189
Opus 5 $0.00031 $0.01094
Sonnet 5 $0.00012 $0.00438
Haiku 4.5 $0.00006 $0.00219

Measured 6d ago against content hash 3b771a43bff6, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

harden 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 6d 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

94% identical to harden — 6 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.

harden/SKILL.md · 354 lines

How it starts

The opening of the file, as written. The whole thing — 354 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Strengthen interfaces against edge cases, errors, internationalization issues, and real-world usage scenarios that break idealized designs.

Assess Hardening Needs

Identify weaknesses and edge cases:

  1. Test with extreme inputs:

    • Very long text (names, descriptions, titles)
    • Very short text (empty, single character)
    • Special characters (emoji, RTL text, accents)
    • Large numbers (millions, billions)
    • Many items (1000+ list items, 50+ options)
    • No data (empty states)
  2. Test error scenarios:

    • Network failures (offline, slow, timeout)
    • API errors (400, 401, 403, 404, 500)
    • Validation errors
    • Permission errors
    • Rate limiting
    • Concurrent operations
  3. Test internationalization:

    • Long translations (German is often 30% longer than English)
    • RTL languages (Arabic, Hebrew)
    • Character sets (Chinese, Japanese, Korean, emoji)
    • Date/time formats
    • Number formats (1,000 vs 1.000)
    • Currency symbols

CRITICAL: Designs that only work with perfect data aren't production-ready. Harden against reality.

Hardening Dimensions

Systematically improve resilience:

Text Overflow & Wrapping

Long text handling:

/* Single line with ellipsis */
.truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* Multi-line with clamp */
.line-clamp {
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Allow wrapping */
.wrap {
  word-wrap: break-word;
  overflow-wrap: break-word;
  hyphens: auto;
}

Flex/Grid overflow:

/* Prevent flex items from overflowing */
.flex-item {
  min-width: 0; /* Allow shrinking below content size */
  overflow: hidden;
}

/* Prevent grid items from overflowing */
.grid-item {
  min-width: 0;
  min-height: 0;
}

Responsive text sizing:

  • Use clamp() for fluid typography
  • Set minimum readable sizes (14px on mobile)
  • Test text scaling (zoom to 200%)
  • Ensure containers expand with text

Read the full file on GitHub · 354 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. 6d ago First seen · 354 lines · 62 tokens per session scan A 3b771a43bff6

Subscribe to this mod's changes

harden is a skill published in the GitHub repository HK-hub/AgentSkills (6 stars, last pushed 22d ago), licensed MIT. It adds 62 tokens to every session and 2,189 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to harden, differing in 6 lines, and is treated as a copy.

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