first-flag（第一面旗帜）

Create first feature flag

The SDK is connected. Now help the user create their first feature flag and see it work end-to-end.

This skill is nested under LaunchDarkly onboarding; the parent Step 6 is first flag. Prior: Apply code changes.

Optional -- Flag Create skill already installed: If the launchdarkly-flag-create skill from github.com/launchdarkly/ai-tooling is available in the session (install with npx skills add launchdarkly/ai-tooling --skill launchdarkly-flag-create -y --agent <agent>), you may use it for creating the flag and choosing evaluation code that matches the repo. You must still complete default off -> verify OFF -> toggle on -> verify ON (Steps 3-5 below). Do not require that skill: this page stays the full fallback when it is missing or MCP-only flows conflict with the user's setup.

Security: Credential handling

Never substitute literal token values into commands. Use environment variable references instead:

• Shell commands: $LAUNCHDARKLY_ACCESS_TOKEN (expanded by the shell, not visible in ps output)
• Set the variable in your session: export LAUNCHDARKLY_ACCESS_TOKEN=<your-token>

This prevents tokens from appearing in process lists, shell history, and screen recordings.

Step 0: Consult SDK flag-key guidance

Before creating the flag or wiring evaluation code, check the Flag key behavior by SDK table below. Some SDKs transform flag keys before exposing them in application code (e.g. the React SDK camelCases kebab-case keys). The flag key you create in LaunchDarkly, the SDK/framework configuration, and the key you reference in code must all align.

• If the SDK transforms keys (e.g. React useFlags() camelCases my-first-flag → myFirstFlag): generate evaluation code using the transformed key. The flag key in LaunchDarkly stays as-is (kebab-case is conventional).
• If the SDK preserves keys as-is (most server-side SDKs): use the exact LaunchDarkly flag key string in code.
• If the SDK supports both modes (e.g. React allows disabling camelCase via provider options): decide which mode the project uses (check existing code or provider config), then generate code that matches.

Flag key behavior by SDK

When wiring the evaluation code in Step 2 below, use the Code key column value, not the raw LaunchDarkly key, whenever the SDK applies a transformation.

Step 1: Create the flag

REST / curl auth: Use $LAUNCHDARKLY_ACCESS_TOKEN as the Authorization header value (LaunchDarkly uses the raw token, no Bearer prefix). The shell expands the variable but doesn't log it.

Via MCP (preferred)

If the LaunchDarkly MCP server is available, use create-feature-flag (or the equivalent flag-creation tool your server exposes):

• Key: my-first-flag (or a name relevant to the user's project)
• Name: "My First Flag"
• Kind: boolean
• Variations: true / false
• Temporary: true

Via LaunchDarkly API

curl -s -X POST \
  "https://app.launchdarkly.com/api/v2/flags/PROJECT_KEY" \
  -H "Authorization: $LAUNCHDARKLY_ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "My First Flag",
    "key": "my-first-flag",
    "kind": "boolean",
    "variations": [
      {"value": true},
      {"value": false}
    ],
    "temporary": true
  }'

Via ldcli

ldcli flags create \
  --access-token "$LAUNCHDARKLY_ACCESS_TOKEN" \
  --project PROJECT_KEY \
  --data '{"name": "My First Flag", "key": "my-first-flag", "kind": "boolean", "temporary": true}'

After creation, the flag starts with targeting OFF, serving the off variation (false) to everyone. When the project key is known, link the user to the flag's dashboard page: https://app.launchdarkly.com/projects/{projectKey}/flags/my-first-flag (substitute the real project key).

Step 2: Add flag evaluation code

Add code to evaluate the flag in the application. Place this where it makes sense for the user's feature.

Server-side examples

// Node.js (@launchdarkly/node-server-sdk) -- ldClient is your initialized server client after waitForInitialization
const context = { kind: 'user', key: 'example-user-key', name: 'Example User' };
const showFeature = await ldClient.boolVariation('my-first-flag', context, false);

if (showFeature) {
  console.log('Feature is ON');
} else {
  console.log('Feature is OFF');
}

# Python (launchdarkly-server-sdk) -- client is ldclient.get() after set_config
from ldclient import Context

context = Context.builder("example-user-key").name("Example User").build()
show_feature = client.variation("my-first-flag", context, False)

if show_feature:
    print("Feature is ON")
else:
    print("Feature is OFF")

// Go
context := ldcontext.NewBuilder("example-user-key").Name("Example User").Build()
showFeature, _ := ldClient.BoolVariation("my-first-flag", context, false)

if showFeature {
    fmt.Println("Feature is ON")
} else {
    fmt.Println("Feature is OFF")
}

Client-side examples

// React — useFlags() camelCases keys: "my-first-flag" → myFirstFlag (see Step 0 table)
import { useFlags } from 'launchdarkly-react-client-sdk';

function MyComponent() {
  const { myFirstFlag } = useFlags();

  return (
    <div>
      {myFirstFlag ? <p>Feature is ON</p> : <p>Feature is OFF</p>}
    </div>
  );
}

The React SDK's useFlags() hook camelCases kebab-case flag keys by default, so my-first-flag becomes myFirstFlag. If the project disables this via reactOptions: {useCamelCaseFlagKeys: false} on the provider, use the original key string instead. Always check the project's provider configuration before choosing which form to use — see the Flag key behavior table above.

Step 3: Verify the default value

With targeting OFF, the flag should evaluate to false. Run the application and confirm:

Feature is OFF

Step 4: Toggle the flag on

Via MCP

The LaunchDarkly MCP server exposes update-feature-flag (JSON Patch), not a tool named toggle-flag -- use the tool names your MCP server lists.

Simplest path: Prefer ldcli or the LaunchDarkly API block below when you only need to turn the flag on once.

If using update-feature-flag: Call it with projectKey, featureFlagKey, and PatchWithComment.patch as a JSON Patch array. Turning the flag on for an environment typically uses a replace operation on that environment's on field (confirm the exact path from get-feature-flag for your account if needed):

{
  "projectKey": "PROJECT_KEY",
  "featureFlagKey": "my-first-flag",
  "PatchWithComment": {
    "patch": [
      {
        "op": "replace",
        "path": "/environments/ENVIRONMENT_KEY/on",
        "value": true
      }
    ],
    "comment": "Onboarding: turn on my-first-flag"
  }
}

Replace ENVIRONMENT_KEY with the environment key for the environment you are targeting (e.g. test, production).

Via LaunchDarkly API

curl -s -X PATCH \
  "https://app.launchdarkly.com/api/v2/flags/PROJECT_KEY/my-first-flag" \
  -H "Authorization: $LAUNCHDARKLY_ACCESS_TOKEN" \
  -H "Content-Type: application/json; domain-model=launchdarkly.semanticpatch" \
  -d '{
    "environmentKey": "ENVIRONMENT_KEY",
    "instructions": [
      {"kind": "turnFlagOn"}
    ]
  }'

Via ldcli

ldcli flags toggle-on \
  --access-token "$LAUNCHDARKLY_ACCESS_TOKEN" \
  --project PROJECT_KEY \
  --environment ENVIRONMENT_KEY \
  --flag my-first-flag

Step 5: Verify the toggle

After toggling the flag on, the application should now show:

Feature is ON

For server-side SDKs using streaming (the default), the change should be reflected within seconds. For client-side SDKs, the change appears on the next page load or when the SDK polls for updates.

Step 6: Add an interactive demo

Now that the flag works, add a visible, interactive element so the user can see the flag in action -- not just a console log. This creates a "wow" moment and gives the user a tangible proof point they can show others.

Choose the right demo based on what you detected:

Frontend demo example (React)

Add a component or element that's visually obvious when the flag is on:

// Add to an existing page component
import { useFlags } from 'launchdarkly-react-client-sdk';

function FeatureFlagDemo() {
  const { myFirstFlag } = useFlags();

  if (!myFirstFlag) return null;

  return (
    <div style={{
      padding: '12px 20px',
      backgroundColor: '#405BFF',
      color: 'white',
      borderRadius: '8px',
      margin: '16px 0',
      fontWeight: 500
    }}>
      LaunchDarkly is working — this banner is controlled by a feature flag
    </div>
  );
}

Place it somewhere visible (e.g., at the top of the main page or in a dashboard/header area).

Backend demo example (Node.js/Express)

Add an endpoint that returns the flag state:

// Add to your Express app (or equivalent for other frameworks)
app.get('/launchdarkly-demo', async (req, res) => {
  const context = { kind: 'user', key: 'demo-user' };
  const flagValue = await ldClient.boolVariation('my-first-flag', context, false);

  res.json({
    flag: 'my-first-flag',
    enabled: flagValue,
    message: flagValue
      ? 'LaunchDarkly is working — the flag is ON'
      : 'LaunchDarkly is working — the flag is OFF'
  });
});

Tell the user to test with: curl http://localhost:PORT/launchdarkly-demo

Backend demo example (Python/Flask)

@app.route('/launchdarkly-demo')
def launchdarkly_demo():
    context = Context.builder("demo-user").build()
    flag_value = ld_client.variation("my-first-flag", context, False)

    return jsonify({
        "flag": "my-first-flag",
        "enabled": flag_value,
        "message": "LaunchDarkly is working — the flag is ON" if flag_value
                   else "LaunchDarkly is working — the flag is OFF"
    })

Full-stack demo

For apps with both server and client (e.g., Next.js, Remix, Rails with frontend):

1. Add the API endpoint (backend example above)
2. Add a UI component that either calls the endpoint or uses the client SDK directly
3. The user can verify both paths work

Guidelines

1. Match existing patterns -- use the same routing style, component conventions, and code style as the rest of the app
2. Make it obvious -- use color, position, or text that clearly indicates this is the LaunchDarkly demo
3. Keep it removable -- add a brief comment like // LaunchDarkly demo - safe to remove so the user knows they can delete it later (or keep it as a template)
4. Don't over-engineer -- this is a demo, not a production feature; a few lines of code is ideal

Walk the user through it

After adding the demo element:

1. Tell the user where you added it and how to see it (URL, page location, command)
2. Have them verify it shows the current flag state
3. Ask them to toggle the flag in the dashboard (provide the deep link: https://app.launchdarkly.com/projects/{projectKey}/flags/my-first-flag)
4. Have them refresh/re-run to see the change
5. Celebrate the successful integration

Congratulations

The user has successfully:

1. Installed the LaunchDarkly SDK
2. Connected it to LaunchDarkly
3. Created a feature flag
4. Evaluated it in code
5. Toggled it and seen the result
6. Added an interactive demo they can show others

This is the "proof point" moment -- the user has a working feature flag they can toggle in real-time. The demo element makes it tangible and shareable.

Encourage the next skill: Suggest they install or enable the launchdarkly-flag-create skill from github.com/launchdarkly/ai-tooling (npx skills add launchdarkly/ai-tooling --skill launchdarkly-flag-create -y --agent <agent>) so future work -- creating flags that match repo conventions, wrapping features, and verifying wiring -- has a dedicated playbook. Offer to help them add it if they are unsure how.

Error handling

Authorization errors

If any step returns a 401 or 403:

D9 -- BLOCKING: Call your structured question tool now.

• question: "I received an authorization error ([specific status code and message]). This requires your action to resolve -- I cannot retry automatically."
• options:

- "I'll re-authenticate -- run ldcli login or refresh my token" - "Let me check my access token and try again" - "I don't have an account -- help me sign up" - "The project or environment doesn't exist -- help me create one"

• STOP. Do not write the question as text. Do not retry authorization errors automatically -- they always require user action. Do not continue until the user selects an option.

Other errors

For non-auth errors (flag creation failures, SDK key mismatches, flags returning fallback values, etc.), diagnose the issue using the error output, application logs, and your understanding of the project.

Next steps to suggest:

• Install launchdarkly-flag-create from github.com/launchdarkly/ai-tooling if it is not already available -- this onboarding flow only covers a first boolean flag; that skill guides real-world flag creation aligned with existing code patterns (requires LaunchDarkly MCP per that skill's prerequisites).
• Use launchdarkly-flag-targeting from the same distribution to set up percentage rollouts and targeting rules
• Read the LaunchDarkly docs for advanced topics like contexts, experimentation, and metrics

Upon completion, continue with: Onboarding summary and Editor rules and skills (default follow-through in the parent onboarding skill -- not MCP setup, which is Step 4). For MCP install or troubleshooting, use mcp-configure and MCP Config Templates.