testing-with-sandbox agent skill by mailtrap
Captures outbound email in development or staging without reaching real recipients, using Mailtrap Email Sandbox to inspect HTML and headers and automate tests.
At a glance
| Publisher | Mailtrap Official |
|---|---|
| Repository | mailtrap/mailtrap-skills (7 listed skills) |
| Category | Testing and QA |
| License | MIT |
| Last commit | October 7, 2026 (repository) |
| SKILL.md | 98 lines, 794 words |
| Bundled files | 1 file |
| Quality score | 80/100 · B Passes all seven graded checks |
| Security scan | Not scanned |
| README badge | Get the badges for this listing |
Before you install
Read from the skill's files at the directory's October 19, 2026 snapshot: what ships with it, what its code reads, and the terms it is published under.
- Bundled scripts: none.
- Credential names SKILL.md mentions:
MAILTRAP_SANDBOX_API_TOKEN,MAILTRAP_API_TOKEN. - License: MIT, an open-source or open-content license.
Install testing-with-sandbox
The skills CLI works with Claude Code, Codex, Cursor and other agents; the other routes copy the folder by hand.
npx skills add https://github.com/mailtrap/mailtrap-skills/tree/main/skills/testing-with-sandboxtmp="$(mktemp -d)"
git clone --depth 1 https://github.com/mailtrap/mailtrap-skills.git "$tmp/repo"
mkdir -p .claude/skills
cp -R "$tmp/repo/"skills/testing-with-sandbox .claude/skills/
rm -rf "$tmp"python3 ~/.codex/skills/.system/skill-installer/scripts/install-skill-from-github.py \
--repo mailtrap/mailtrap-skills \
--path skills/testing-with-sandboxmailtrap/mailtrap-skills is third-party code. Read SKILL.md and any bundled scripts before you install it.
How the author describes it
Use when capturing outbound email in development or staging without delivering to real recipients, inspecting HTML or headers, running spam or structure checks, or automating tests against a fake inbox. Use when testing outgoing mail from an app without committing to a production ESP yet. Use when using Mailtrap Email Sandbox, Sandbox API, or sandbox-mode sending.
From the description field of SKILL.md. Agents read this line to decide when to load the skill.
Sections in SKILL.md
- Overview
- When to use
- When not to use
- Quick reference
- API base
- Tokens and accountid
- When to use API vs SMTP
- SMTP settings (sandbox)
- Key parameters
- Typical use cases
- Example API paths
- SDKs
- Common mistakes
- Sandbox email address
Files in the skill folder
SKILL.md
Suede Skill Check: 80/100 · B
Report snapshot · · graded-v2
The rubric totals 100 points; published scores are capped at 99. Security scan: not scanned.
Source revision: 2c95794d19d1. Report version ffdf8831010b. Badge URLs follow the latest listing; save the report to keep this version.
Download report · Request a fresh review
What to review next
- Boundary clause: 0 of 4 points. 4 when the description says when not to use the skill (“Not for …”, “Do not use …”, “Use … instead”).
- Example request: 0 of 3 points. 3 when the description quotes an example request (3–60 characters in quotation marks).
- Reference files: 0 of 3 points. 3 when the skill folder ships a references/, reference/ or docs/ folder.
Add declarations and bundled files when they describe the skill’s actual needs. Update the source, then request a fresh review with the changed commit or PR.
testing-with-sandbox passes the required frontmatter check and all seven graded checks, which cover the SKILL.md format, a declared license and a commit in the last year. Those checks earn 56 of the score’s points; the rest come from description quality, instruction depth, bundled files, maintenance and curated-list citations. How the score works.
See the checks and points
| Check | Result |
|---|---|
| Frontmatter parses and declares a name and a description | Pass |
| Name uses lowercase letters, digits and hyphens, 64 characters or fewer | Pass |
| Name matches the skill's folder name | Pass |
| Description is between 50 and 1,024 characters | Pass |
| Description says when an agent should use the skill | Pass |
| SKILL.md body is 500 lines or fewer | Pass |
| A license is declared in the frontmatter or the repository | Pass |
| Repository has a commit in the last 12 months | Pass |
| Score component | Points |
|---|---|
| Structural checks | 56 of 56 |
| Description length | 5 of 5 |
| Boundary clause | 0 of 4 |
| Example request | 0 of 3 |
| Instruction depth | 7 of 7 |
| Reference files | 0 of 3 |
| Bundled scripts | 0 of 2 |
| Recent maintenance | 9 of 9 |
| Curated-list citations | 3 of 7 |
| Tool permissions declared | 0 of 2 |
| Compatibility declared | 0 of 2 |
Two badges for testing-with-sandbox
Choose the numeric badge, the letter badge, or both. Each links to this skill’s Suede listing; either valid linked badge can qualify for the feature offer.
[](https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/)
[](https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/)<a href="https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/"><img src="https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/score.svg" alt="Suede Skill Check: 80/100" width="160" height="175"></a>
<a href="https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/"><img src="https://skills.suedeai.ai/directory/mailtrap/mailtrap-skills/testing-with-sandbox/badge.svg" alt="Suede Skill Check: Grade B" width="160" height="175"></a>Suede Certified on the shield refers to this published structural quality check. Security scan: not scanned. Read the methodology.
Limited-time feature offer: display either the numeric or letter badge in your repository or skill README (both also qualify), then request badge verification. Eligible skills scoring 80–99 can receive a featured placement after Suede verifies at least one valid badge linked to the skill’s listing. Suede has not announced an end date.
Where this skill is cited
mailtrap/mailtrap-skills appears in 2 curated lists: BehiSecc/awesome-claude-skills, VoltAgent/awesome-agent-skills.