What is add-private-feature-flag?

A coding checklist for adding a private feature flag to Ghost, a publishing platform. It covers registering the flag and adding its toggle to the developer-only Labs settings.

Use it when adding a developer experiment that should appear under Ghost’s “Private features” settings. It also guides the required unit tests, end-to-end tests, and snapshot review.

It prevents the server setting and Admin interface from getting out of sync, and reminds you to run the relevant tests and update their snapshots.

add-private-feature-flag — Skill by TryGhost

Install

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.

agentmods

npx agentmods add skills/tryghost/ghost/add-private-feature-flag

Any agent

npx skills add TryGhost/Ghost --skill add-private-feature-flag

Clone the repo

git clone --depth 1 https://github.com/TryGhost/Ghost

Made for: Claude Code, Codex.

Per session 30 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 430 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00030	$0.00430
Opus 5	$0.00015	$0.00215
Sonnet 5	$0.00006	$0.00086
Haiku 4.5	$0.00003	$0.00043

Measured 3d ago against content hash 52ce10961d25, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

add-private-feature-flag 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 3d ago.

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.

.agents/skills/add-private-feature-flag/SKILL.md · 35 lines

What it actually says

Add Private Feature Flag

Overview

Adds a new private feature flag to Ghost. Private flags appear in Labs settings under the "Private features" tab, visible only when developer experiments are enabled.

Read and follow the canonical feature flag guide before adding a flag. The guide covers when a Labs flag is appropriate, safe gating across server and Admin, testing, and the cleanup lifecycle.

Steps

Add the flag to ghost/core/core/shared/labs.js
- Add the flag name (camelCase string) to the PRIVATE_FEATURES array.
Add a UI toggle in apps/admin/src/settings/advanced/labs/private-features.tsx
- Add a new entry to the features array with title, description, and flag (must match the string in labs.js).
Run tests and update the config API snapshot
- Unit: cd ghost/core && pnpm test:single test/unit/shared/labs.test.js
- Update snapshots: cd ghost/core && pnpm test:single test/e2e-api/admin/config.test.js -u && pnpm test:single test/e2e-api/admin/settings.test.js -u
- Review both snapshot diffs to confirm only your new flag was added.

Notes

No database migration is needed. Labs flags are stored in a single JSON labs setting.
The flag name must be identical in labs.js, private-features.tsx, and the snapshots.
Flags are camelCase strings (e.g. welcomeEmailDesignCustomization).
For public beta flags (visible to all users), add to PUBLIC_BETA_FEATURES in labs.js instead and add the toggle to apps/admin/src/settings/advanced/labs/beta-features.tsx.

Changes

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.

3d ago First seen · 35 lines · 30 tokens per session scan A 52ce10961d25

Subscribe to this mod's changes

add-private-feature-flag is a skill published in the GitHub repository TryGhost/Ghost (55,095 stars, last pushed yesterday), licensed MIT. It adds 30 tokens to every session and 430 once invoked, about $0.0002 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 2026-08-30.

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