spike-then-harden

spike-then-harden is an agent for Claude Code from SeongwoongCho/adaptive-harness. It costs 34 tokens per session (72 once invoked), scanned A, original, MIT.

A two-stage coding agent that first builds a quick disposable prototype, then rewrites it for production use based on what it learned.

In plain words
What is it for?
Investigating an unfamiliar problem quickly and then producing a more robust production-quality solution.
Why use it?
It separates early exploration from final implementation, reducing the risk of committing to an unclear design too soon.

Agent for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: model in frontmatter.

Part of the adaptive-harness plugin — 4 skills, 4 commands, 29 agents, 5 hooks shipped together

Good fit Investigating an unfamiliar problem quickly and then producing a more robust production-quality solution.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/seongwoongcho/adaptive-harness/spike-then-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.

Clone the repo
git clone --depth 1 https://github.com/SeongwoongCho/adaptive-harness

Made for: Claude Code.

Or install adaptive-harness, the plugin that ships this one along with the rest of its 4 skills, 4 commands, 29 agents, 5 hooks.

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 spike-then-harden

README.md
[![agentmods](https://agentmods.dev/badge/agents/seongwoongcho/adaptive-harness/spike-then-harden/github.svg)](https://agentmods.dev/agents/seongwoongcho/adaptive-harness/spike-then-harden)
Your own site
<a href="https://agentmods.dev/agents/seongwoongcho/adaptive-harness/spike-then-harden"><img src="https://agentmods.dev/badge/agents/seongwoongcho/adaptive-harness/spike-then-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 spike-then-harden

Your own site · 80×15
<a href="https://agentmods.dev/agents/seongwoongcho/adaptive-harness/spike-then-harden"><img src="https://agentmods.dev/badge/agents/seongwoongcho/adaptive-harness/spike-then-harden.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 34 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 72 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 $0.00034 $0.00072
Opus 5 $0.00017 $0.00036
Sonnet 5 $0.00007 $0.00014
Haiku 4.5 $0.00003 $0.00007

Measured 12d ago against content hash 21c6998eae0f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

spike-then-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 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.

agents/spike-then-harden.md · 8 lines

What it actually says

You are the Spike-Then-Harden harness agent. Your full instructions are provided in the task prompt.

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 · 8 lines · 34 tokens per session scan A 21c6998eae0f

Subscribe to this mod's changes

spike-then-harden is an agent published in the GitHub repository SeongwoongCho/adaptive-harness (8 stars, last pushed 5mo ago), licensed MIT. It adds 34 tokens to every session and 72 once invoked, about $0.0002 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.