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 agentmods add skills/outlinedriven/outline-driven-development/atherisnpx skills add OutlineDriven/outline-driven-development --skill atherisgit clone --depth 1 https://github.com/OutlineDriven/outline-driven-developmentWrote 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/outlinedriven/outline-driven-development/atheris)<a href="https://agentmods.dev/skills/outlinedriven/outline-driven-development/atheris"><img src="https://agentmods.dev/badge/skills/outlinedriven/outline-driven-development/atheris.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00062 | $0.01920 |
| Opus 5 | $0.00031 | $0.00960 |
| Sonnet 5 | $0.00012 | $0.00384 |
| Haiku 4.5 | $0.00006 | $0.00192 |
Grade A, and why
atheris 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 yesterday.
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 — 78 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Atheris
Contract
| Field | Bound contract |
|---|---|
| Trigger | User needs coverage-guided fuzzing for Python code or a Python native extension using Atheris. |
| Authority | Write the Atheris harness file, a corpus directory, the local fuzzing process, and when required for dependency management, create or modify pyproject.toml and uv.lock in the harness directory. Roll back by deleting the harness file and corpus directory and restoring pyproject.toml and uv.lock to their pre-run state; no source under test is mutated. |
| Side effect | Local writes: a fuzz.py (or named) harness, a corpus/ directory of seed and crash artifacts, and a transient fuzzing process. |
| Done | Atheris executes an instrumented target through a deterministic TestOneInput harness, reports coverage, and any saved crash artifact reproduces the same failure when replayed. |
Inputs
- Target: the Python function or module to fuzz, or the Python C extension to fuzz. Required.
- Target kind: pure Python, or native C extension. Required; it selects the instrumentation and build path.
- Expected exceptions: the exception types the target legitimately raises on bad input, so the harness catches them instead of crashing. Optional but recommended.
- Seed corpus: initial input files for
corpus/. Optional; Atheris can start empty. - Time/length budget:
-max_total_timeand-max_lenvalues. Optional; defaults are libFuzzer defaults. - Sanitizers: whether AddressSanitizer and/or UndefinedBehaviorSanitizer are enabled. Optional; ASan is the default for native extensions.
Procedure
-
Determine target kind. If the target is pure Python, follow the pure-Python path. If it is a C extension compiled from source, follow the native-extension path. Do not guess; ask the user when the kind is ambiguous.
-
Install Atheris. If the harness directory is not already a uv project (no
pyproject.tomlpresent), runuv init --bareonce. Thenuv add atheris. Verify withpython -c "import atheris; print(atheris.__version__)".
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- yesterday First seen · 78 lines · 62 tokens per session scan A 18e7afae2e02
atheris is a skill published in the GitHub repository OutlineDriven/outline-driven-development (52 stars, last pushed yesterday), licensed Apache-2.0. It adds 62 tokens to every session and 1,920 once invoked, about $0.0003 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 2026-09-03.
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