A workflow for Go fuzz testing, which repeatedly gives varied and unexpected inputs to code to find crashes and other failures. It runs existing fuzz targets, adds new targets, and investigates failures.

Use it to fuzz ELPS packages, add or change fuzz targets, or investigate a fuzzing failure.

Fuzzing can find input combinations that hand-written tests miss. Replaying saved failing inputs helps prevent a fixed crash from returning.

How luthersystems/elps configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to luthersystems/elps. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/luthersystems/elps/main/.claude/skills/fuzz/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/luthersystems/elps

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/luthersystems/elps/fuzz/github.svg)](https://agentmods.dev/skills/luthersystems/elps/fuzz)

Your own site

<a href="https://agentmods.dev/skills/luthersystems/elps/fuzz"><img src="https://agentmods.dev/badge/skills/luthersystems/elps/fuzz/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/luthersystems/elps/fuzz"><img src="https://agentmods.dev/badge/skills/luthersystems/elps/fuzz.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,255 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.

Model	Per session	Once invoked
Fable 5.1	$0.00000	$0.01255
Opus 5.5	$0.00000	$0.00502
Sonnet 5.5	$0.00000	$0.00251
Haiku 4.5	$0.00000	$0.00126

Measured 2d ago against content hash ec04954b116f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

fuzz 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 2d 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.

.claude/skills/fuzz/SKILL.md · 93 lines

How it starts

The opening of the file, as written. The whole thing — 93 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/fuzz — Native Go Fuzzing Skill

Runs the repository's go test -fuzz targets, adds new ones, and triages crashers. CI runs .github/workflows/fuzz.yml: 30s per target on PRs, 10m per target nightly, sharded.

Trigger

Use when asked to fuzz, add or change a fuzz target, investigate a fuzz CI failure, or triage a file under some package's testdata/fuzz/<Target>/.

Run

make fuzz-list                                  # authoritative list of targets (discovered with go test -list)
make fuzz                                       # every target, 30s each (the PR budget)
make fuzz FUZZTIME=10m                          # the nightly budget
make fuzz FUZZ_PKGS=./parser/rdparser/...       # one package
go test -run='^$' -fuzz='^FuzzEval$' -fuzztime=60s ./lisp/   # one target by hand

scripts/fuzz.sh refuses to run without a parsable FUZZTIME and caps every invocation with a hard -timeout; never write a -fuzz invocation without -fuzztime (CI checks for that). FUZZ_TAGS=elpscheck fuzzes the tagged build, whose targets are otherwise invisible.

Plain go test ./... (and so make test) replays every committed seed and crasher in testdata/fuzz/ as a regression case.

Triage a crasher

Find it: go test -fuzz writes testdata/fuzz/<Target>/<hash> in the target's package; CI uploads the same file as an artifact.
Reproduce without fuzzing: go test -run='^<Target>$/^<hash>$' ./<pkg>/.
Classify: a real defect in the code under test, a harness defect (budget too small for a terminating program, a watchdog on wall clock), or a toolchain race. make fuzz-classify-test covers how scripts/fuzz.sh reports each; read its output before assuming the product is at fault.
Fix the root cause with a focused regression test, and commit the crasher file so go test keeps replaying it.

Add a target

Put it in the package's fuzz_test.go (or <area>_fuzz_test.go), named FuzzXxx. Discovery is automatic — there is no registration table.
Seed from internal/fuzzseed (All(), LispSources(), Adversarial(), Pathological()) plus target-specific adversarial input.
Assert a property with teeth (round-trip equality, no internal panic, termination), not merely "did not crash".
Any termination watchdog must use internal/fuzzwatch (scheduled-time budget, with a floor enforced by its call-site guard test), not a bare time.After.
Run make fuzz-budget-check: each new target adds a FUZZTIME to the nightly sweep, and the check derives whether fuzz.yml's timeout-minutes still holds. Follow its printed options rather than raising the timeout by hand.
After touching scripts/fuzz.sh or fuzz.yml, run make ci-gates-test and make fuzz-classify-test.

Read the full file on GitHub · 93 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.

2d ago First seen · 93 lines · 0 tokens per session scan A ec04954b116f

Subscribe to this mod's changes

fuzz is a skill published in the GitHub repository luthersystems/elps (36 stars, last pushed today), licensed BSD-3-Clause. It costs nothing until one of its globs matches a file; then it loads 1,255 tokens. 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 2026-10-26.

Go Testing embedded-language go lisp

code-guidelines-go

Go 1.24–1.27 coding guidelines for the dimetron/pi-go AI agent runtime. Use this skill whenever writing, reviewing, or refactoring ANY Go code in pi-go. This covers idiomatic style, error handling, concurrency, project layout, testing (table-driven, fuzz, benchmarks, synctest), new stdlib usage, golangci-lint v2…

dimetron/pi-go · 124 tokens

go-127

What changed in Go 1.27 (released August 2026) and how it changes the way Go is written in pi-go. Use this skill when writing or reviewing Go that could use a 1.27 feature, when bumping the go directive in go.mod, when a build or test behaves differently after a toolchain upgrade, or when code-guidelines-go points…

dimetron/pi-go · 177 tokens

bubbletea-testing

Use this skill whenever writing tests for Bubble Tea (charmbracelet/bubbletea) TUI applications in Go. Triggers include any mention of testing Bubble Tea models, teatest, golden file testing for TUIs, testing tea.Cmd or tea.Msg, snapshot testing terminal output, or writing tests for any Go CLI/TUI that uses the Elm…

dimetron/pi-go · 139 tokens

vhs-e2e-gif

Record a test run, a TUI session, or any terminal command as a GIF with VHS and attach it to a GitHub PR as a release-hosted asset, never a repo commit. Use when asked to record an e2e run, demo a fix on a PR, attach a GIF or screen recording to a pull request, show a test passing visually, or produce a terminal…

dimetron/pi-go · 106 tokens

check-linters-before-commit

Before any commit, run linters, vet, tests, and build verification; do not commit until checks pass.

dimetron/pi-go · 30 tokens

ci-orchestrator

Run a CI-like pipeline locally (format, lint, vet, static-analysis, tests) and summarize per-step results with remediation guidance.

pilinux/gorest · 32 tokens

elps: Skill for Claude Code