harness-writing

Designs and improves fuzzing harnesses for C/C++ and Rust. Covers mapping raw bytes onto a target API, generating structured inputs, avoiding non-determinism and false crashes, and deciding what to fuzz together. Use when writing a first LLVMFuzzerTestOneInput or fuzz_target! harness, when a campaign finds nothing or reports crashes that will not reproduce, or when the target API needs structured rather than raw input.

Agent Skill from trailofbits/skills

Copilot Studio

Passes documented load rules

No documented load rule failed.

Microsoft 365 Copilot Preview, Frontier tenants only

Needs changes

Fails: Instructions are under 20,000 characters (M365-INSTRUCTIONS)
instructions are 20,738 characters
rule · Microsoft 365 Copilot: What is a skill
Fails: Every file has a supported file type (M365-FILE-TYPES)
1 unsupported: assets/trail-of-bits-mark.svg
rule · Microsoft 365 Copilot: Supported file and script types

An agent can have at most 8 skills. Custom skills aren't available in tenants that use Microsoft Purview Information Barriers.

Compatible isn't the same as safe. These verdicts only say whether a skill's files follow Microsoft's documented load rules. The checker reads files and never runs them, and it doesn't review what a skill or its scripts actually do. Read a skill's instructions and scripts before you add it to an agent.

Standards signals

Meets the agentskills.io required fields.

Frontmatter	Present and parsed Spec: frontmatter
name	Meets the spec (1-64 chars, a-z 0-9 hyphens) Spec: name
description	Present, 1-1,024 characters Spec: description
compatibility	Absent or under 500 characters Spec: compatibility
Name matches folder	Yes (`harness-writing`) Spec: name

Observed from the public SKILL.md at the commit above on 2026-10-23. Not a certification: AAIF and the Agent Skills project don't certify skills. Validate your own skill with skills-ref validate.

Source repo	trailofbits/skills
Path	plugins/testing-handbook-skills/skills/harness-writing/SKILL.md
Commit checked	`1e0cb77d071a`
Repo license	CC · we list metadata only
Files	3
Scripts	None
Instructions	20,738 characters
Deepest folder	1 below the skill folder
Rules version	2026-10-22

Re-check the latest version How skill checks work

Is this wrong or out of date? Email us. Skills data built 2026-10-23; rules as of 2026-10-22.

Rule-based checks of public files against Microsoft's documented load rules, not tested in Copilot Studio or Microsoft 365 Copilot. Independent project, not affiliated with Microsoft.