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.
npx skills add provos/ironcurtain --skill harness-design-fuzzinggit clone --depth 1 https://github.com/provos/ironcurtainWrote 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.
[](https://agentmods.dev/skills/provos/ironcurtain/harness-design-fuzzing)<a href="https://agentmods.dev/skills/provos/ironcurtain/harness-design-fuzzing"><img src="https://agentmods.dev/badge/skills/provos/ironcurtain/harness-design-fuzzing/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.
<a href="https://agentmods.dev/skills/provos/ironcurtain/harness-design-fuzzing"><img src="https://agentmods.dev/badge/skills/provos/ironcurtain/harness-design-fuzzing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
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 →
- medium Output Handling · line 141 Output size or generation rate is not bounded. Unbounded output enables denial-of-service through resource exhaustion, log flooding, or context-window stuffing.Fix: Set explicit limits on output length, generation count, and rate. Use max_tokens and truncation to prevent unbounded output.
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 | $0.00147 | $0.04708 |
| Opus 5 | $0.00073 | $0.02354 |
| Sonnet 5 | $0.00029 | $0.00942 |
| Haiku 4.5 | $0.00015 | $0.00471 |
Grade A, and why
harness-design-fuzzing 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.
How it starts
The opening of the file, as written. The whole thing — 207 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Harness Design for Vulnerability Discovery
Reference vocabulary for designing instrumented harnesses that drive vulnerability discovery. Catalogs the classes, scopes, instrumentation choices, and pitfalls a harness design needs to reason about.
A harness is not a unit test. The point of a harness is to systematically explore an input space against an oracle that fires on a violation — not to confirm a few hand-picked cases. Hand-picked scenarios miss boundary values; the boundary is where the bug lives.
Design class — pick first
Every harness has exactly one of two design classes. The class drives the sweep variables and the oracle. Tier (below) is orthogonal — any tier can be either class.
-
Trigger-driven. The directive supplies a falsifiable claim with a named violation site — a specific function, value range, and expected oracle (a bounds check fires, a type narrows lossily, a sentinel collides, a state-machine transition is reached out of order). The harness sweeps the hypothesis input variables. The oracle is the named violation pattern firing.
-
Coverage-driven. The directive supplies an under-exercised dispatch surface — a code region the project's existing fuzzers don't reach, with named dispatch axes (option flags, message types, opcode tables, mode bits, format variants) the input space hasn't crossed. The harness sweeps the dispatch axes. The oracle is any sanitizer error within the named region. The named region must be a concrete file/function set, not "somewhere in the target."
Pick coverage-driven when prior trigger-driven rounds against the same region have been mitigated by upstream guards but the region itself is untested by the existing fuzz infrastructure. Pick trigger-driven when there is a specific theory to falsify.
Harness tiers
Three tiers of infrastructure scope. Match tier to hypothesis scope; never use Tier 1 for a cross-component target.
Tier 1 — Isolated function test
Extract the relevant function(s) into a standalone, self-contained program. Copy the exact types, macros, and helper functions verbatim from the source. Stub only I/O, networking, and allocation.
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.
- 12d ago First seen · 207 lines · 147 tokens per session scan A b014cc35478e
harness-design-fuzzing is a skill published in the GitHub repository provos/ironcurtain (604 stars, last pushed today), licensed Apache-2.0. It adds 147 tokens to every session and 4,708 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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