How do I install the Feature Flag skill?

Run npx skillmds@latest add elastic/feature-flag in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Feature Flag safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Feature Flag?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Feature Flag free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Feature Flag?

elastic (@elastic) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Feature Flag by elastic — Agent Skill

Name: Feature Flag
Author: elastic

Feature Flag

Registers a feature flag as additive-only and verifies the flag-off path still matches the previous default. Use whenever adding or extending a feature flag, editing FeatureFlags.cs, changing feature_flags in assembler.yml, gating a code path behind a FEATURE_* environment variable, or enabling a flag in an environment. Do not skip this skill for flag work even if the user does not name it.

elastic 9ae4e05 2.9 KB Updated Sep 17, 2026

File contents

Feature Flag Skill

A feature flag is additive. Flag off keeps the previous default. Flag on adds new behavior only.

When to use

Read this skill before you add any of these:

A typed flag on FeatureFlags
A feature_flags YAML key
A FEATURE_* environment override
An if (flag) around a code path

How flags work

Typed flags live in src/Elastic.Documentation.Configuration/Builder/FeatureFlags.cs
Keys normalize to kebab-case. The env override is FEATURE_<UPPER_SNAKE>
Per-environment YAML keys live under feature_flags in config/assembler.yml as UPPER_SNAKE
Flags stay off unless listed. Do not enable a new flag in prod when you create it
PublishEnvironment.ToFeatureFlags() in src/Elastic.Documentation.Configuration/Assembler/PublishEnvironment.cs loads YAML keys through Set()
Follow the test pattern in tests/Elastic.Documentation.Build.Tests/FeatureFlagsTests.cs

Steps

1. Additive means

Flag off equals the previous default in behavior. Flag on adds new behavior only.

Do not move, hide, relocate, or delete existing output when you introduce the flag.

New behavior is a new panel, a new build step, or a new field. It is not a relocated copy of something that already shipped.

2. Register the flag

Add a typed property on FeatureFlags. The default stays false.
Add YAML keys only in the environments that opt in.
Do not turn the flag on in prod as part of creating it.

3. Gate only the new path

Put the if (flag) around new code. Leave the existing branch as it was.

Shared markup, layout, and data wiring that the old path still needs stay outside the flag.

4. Verify additivity before you finish

This step is required. Do not skip it.

List every existing surface the change touches. Include render paths, CLI output, build steps, API payloads, mobile and desktop, and assembler vs isolated builds.
For each surface, compare the flag-off branch to the pre-change code or output.
If anything that already shipped is missing, moved, or changed when the flag is off, stop. Restore it on the default path.

5. Prove it with tests

The flag defaults to false.
Flag-off preserves existing behavior.
Flag-on shows the new behavior.
Sibling flags stay unchanged.
Prod, or the default environment, does not enable the new flag.

6. Stop conditions

Do not ship a flag whose existing behavior lives only on the new path.

Do not treat "the new path has it" as coverage for the old path.

---name: feature-flagdescription: Registers a feature flag as additive-only and verifies the flag-off path still matches the previous default. Use whenever adding or extending a feature flag, editing FeatureFlags.cs, changing feature_flags in assembler.yml, gating a code path behind a FEATURE_* environment variable, or enabling a flag in an environment. Do not skip this skill for flag work even if the user does not name it.---# Feature Flag SkillA feature flag is additive. Flag off keeps the previous default. Flag on adds new behavior only.## When to useRead this skill before you add any of these:- A typed flag on `FeatureFlags`- A `feature_flags` YAML key- A `FEATURE_*` environment override- An `if (flag)` around a code path## How flags work- Typed flags live in `src/Elastic.Documentation.Configuration/Builder/FeatureFlags.cs`- Keys normalize to kebab-case. The env override is `FEATURE_<UPPER_SNAKE>`- Per-environment YAML keys live under `feature_flags` in `config/assembler.yml` as `UPPER_SNAKE`- Flags stay off unless listed. Do not enable a new flag in `prod` when you create it- `PublishEnvironment.ToFeatureFlags()` in `src/Elastic.Documentation.Configuration/Assembler/PublishEnvironment.cs` loads YAML keys through `Set()`- Follow the test pattern in `tests/Elastic.Documentation.Build.Tests/FeatureFlagsTests.cs`## Steps### 1. Additive meansFlag off equals the previous default in behavior. Flag on adds new behavior only.Do not move, hide, relocate, or delete existing output when you introduce the flag.New behavior is a new panel, a new build step, or a new field. It is not a relocated copy of something that already shipped.### 2. Register the flag1. Add a typed property on `FeatureFlags`. The default stays false.2. Add YAML keys only in the environments that opt in.3. Do not turn the flag on in `prod` as part of creating it.### 3. Gate only the new pathPut the `if (flag)` around new code. Leave the existing branch as it was.Shared markup, layout, and data wiring that the old path still needs stay outside the flag.### 4. Verify additivity before you finishThis step is required. Do not skip it.1. List every existing surface the change touches. Include render paths, CLI output, build steps, API payloads, mobile and desktop, and assembler vs isolated builds.2. For each surface, compare the flag-off branch to the pre-change code or output.3. If anything that already shipped is missing, moved, or changed when the flag is off, stop. Restore it on the default path.### 5. Prove it with tests- The flag defaults to false.- Flag-off preserves existing behavior.- Flag-on shows the new behavior.- Sibling flags stay unchanged.- Prod, or the default environment, does not enable the new flag.### 6. Stop conditionsDo not ship a flag whose existing behavior lives only on the new path.Do not treat "the new path has it" as coverage for the old path.

Frequently asked questions