API Test Mode Skill: What It Does and How to Install It

Helps you design the test mode or sandbox that outside developers build against before touching real money or data.

Installs: 9.6K; on skills.sh
Stars: 9; on GitHub
Files: 4; besides SKILL.md
Updated: Nov 2026; last repo commit

api-test-mode-design makes Claude act as a test-mode designer for an API platform. It covers the isolation boundary (a soft test-mode toggle or a hard separate-copy sandbox), test-key prefixes, deterministic test values, simulated events and time, quotas, abuse controls, and the graduation path to live.

It loads when you mention a sandbox, test mode, test API keys, magic test values, simulated webhook events or demo data. It does not cover code-execution sandboxing or unit-test mocking. It bundles three reference files and no scripts.

Good for

API teams adding a sandbox or test mode
Payments and billing platforms where integrators need safe test runs
Developer-experience leads defining the path from test to live

Install api-test-mode-design

Claude Code

Copy this prompt.

Install the api-test-mode-design skill in Claude Code. Run this command:

/plugin marketplace add samber/developer-platform-skills
/plugin install developer-platform-skills@developer-platform-skills

Then check that it loaded and tell me how to use it.

2
Paste it into Claude Code. It shows the change and asks before running it.

The README installs every skill in the repo (61 skills/*/SKILL.md in the git tree), because skills here reference each other. api-test-mode-design is one of them. Pick one route, not both.

From the project README. Source.

What's in the skill

When it loads

Design the test/sandbox mode of a public API platform so external integrators build and validate without touching real money, messages, or data - isolation architecture (soft test-mode toggle vs hard separate-copy sandbox), test-key prefixing, magic test values, simulated objects and personas, on-demand test events, deterministic time manipulation, reset and seeding, sandbox quotas, abuse controls, and graduation to live. Use whenever the user mentions a sandbox, test mode, test API keys, magic or dummy test values, simulated webhook events, or demo data - even if they never say "test mode". Not code-execution sandboxing or unit-test mocking. Do NOT use for partner sandbox provisioning - use samber/developer-platform-skills@partner-app-onboarding instead.

Sections in SKILL.md

Scope
Clarifying questions
Product domain split
Workflow
1. Choose the isolation model
2. Make every failure path triggerable
3. Simulate events and time
4. Harden credentials, quotas, and abuse controls
5. Design the graduation path
Failure modes
Measurement
Invocation examples
References

Key facts

Author: Samuel Berthe
Repo: samber/developer-platform-skills, which holds 61 skills
License: MIT (LICENSE, README, plugin.json and SKILL.md all say MIT)
Version in SKILL.md: 1.0.2
Installs on skills.sh: 9,631 (Nov 2, 2026)
GitHub stars (repo): 9 (Nov 2, 2026)
Last commit (repo): Nov 1, 2026
What installs: 5 files including SKILL.md: 3 reference files and evals/evals.json; no scripts
Needs: The other skills in the repo; the README says to install all of them
Works in: Claude.ai, Claude Code, Codex, Cursor, Gemini CLI, and tools that read skills.sh installs

What it includes

Asks seven questions before designing anything.
Try: “Choose between a test-mode toggle and a fully separate sandbox environment for our new public API, and design the graduation path to live.”
Clarifying questions
Decides between a test-mode toggle and a fully separate sandbox.
1. Choose the isolation model
Designs deterministic test values and simulated objects so integrators can hit each error.
Uses magic-value catalogs from references/magic-value-catalogs.md.
2. Make every failure path triggerable
Designs on-demand test events, time manipulation, reset and seeding.
3. Simulate events and time
Covers test-key prefixes, sandbox quotas and abuse controls.
Pairs with api-auth-key-management for the key prefix scheme.
4. Harden credentials, quotas and abuse controls
Writes the compliance gate, cutover checklist and canary for going live.
Details are in references/graduation-gates-and-cutover-checklist.md.
5. Design the graduation path

From the official docs

Permissions

Low risk

This skill writes design advice and bundles no scripts, so the main thing to watch is where your agent saves notes.

What it can do

Read your data
Create and change things
Delete things
Read-only mode

Watch out for

It may save notes to developer-platform-context.md
SKILL.md says that when your agent keeps memory in a file, it should consider using this file name. Our advice: keep it out of commits if it holds company plans. github.com

Technical details

Scopes	Asks you interview questions and writes a design document from your answers

Questions

How do I install api-test-mode-design?

Use the install box at the top of this page. The README says to install every skill in samber/developer-platform-skills, not one, because the skills hand work to each other. Pick one route per agent.

Does api-test-mode-design work in Claude, Codex and Cursor?

The README documents install routes for Claude.ai (plugin marketplace), Claude Code, Codex, Cursor, Gemini CLI and the skills.sh CLI. The install box lists each one.

What does it ask me before it designs anything?

SKILL.md lists seven questions to ask first, and the answers change the later steps. Have your current setup and constraints ready.

Does it run scripts or need an API key?

It bundles no scripts. The folder holds SKILL.md, reference Markdown files and an evals file, and the skill works by asking you questions and writing advice.

Is api-test-mode-design safe to install?

It bundles no scripts, so installing it adds instructions and reference files rather than programs. SKILL.md also suggests that, if your agent keeps notes in a file, it uses developer-platform-context.md. Our advice: keep that file out of public commits if it holds company plans, and check any figures the skill cites against their sources before quoting them to customers.

How is it different from partner-app-onboarding?

api-test-mode-design designs the sandbox itself. SKILL.md says not to use it for partner sandbox provisioning and points to partner-app-onboarding for that.

Information

updated Nov 2, 2026

Repository: samber/developer-platform-skills
Folder: skills/api-test-mode-design

samber/developer-platform-skills skills.sh

Sources

Docs, issue trackers and discussions this page is built from.

Show all 2

samber/developer-platform-skills README · github.com
api-test-mode-design SKILL.md · github.com