constant-time-testing

Measures timing side channels in cryptographic implementations by running them, using dudect for statistical analysis and Timecop over Valgrind for dynamic tracing. Covers the formal, symbolic, dynamic, and statistical tool categories and how to read a result. Use when testing whether a running implementation is constant-time, measuring timing variance on a compiled binary, or investigating a suspected timing attack. Not for statically inspecting compiler output — the constant-time-analysis plugin covers that.

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 20,410 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 (`constant-time-testing`) 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/constant-time-testing/SKILL.md
Commit checked	`1e0cb77d071a`
Repo license	CC · we list metadata only
Files	3
Scripts	None
Instructions	20,410 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Is this wrong or out of date?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.