---
title: "Keep every flag in one register · Agent Wranglers"
url: https://agentwranglers.se/playbook/engineering/feature-flags/flag-register
id: ENG-45
level: Recommended
updated: 2026-10-22
tokens: 1128
licence: "CC BY 4.0"
licence_url: https://creativecommons.org/licenses/by/4.0/
---

# Keep every flag in one register

For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Feature flags](https://agentwranglers.se/playbook/engineering/feature-flags.md).

By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-22.

- ID: ENG-45
- Level: Recommended
- Chapter: [Feature flags](https://agentwranglers.se/playbook/engineering/feature-flags.md)
- Rule: List every feature flag in one file in the repository, with its type, owner, creation date and expiry or review date. A flag that is not in the register cannot be read by the code.
- Check: A build step lists every flag name the code reads. It fails when one is missing from the register or lacks a type, owner, creation date or expiry. It also fails on a register entry the code no longer reads.
- How: Give each flag one of four types, because each lives for a different time. A release flag hides unfinished work and lives for weeks. An experiment flag runs an A/B test and ends with it. A kill switch turns off a feature under load, and a permission flag limits a feature to some customers. Kill switches and permission flags live for years, so give them a yearly review date instead of an expiry. Unleash, for example, marks release and experiment flags as stale after 40 days by default. Remove expired flags as [Remove flags that never change](https://agentwranglers.se/playbook/architecture/dead-code/remove-stale-flags.md) says. Pick the flag tool with [the feature flags pick](https://agentwranglers.se/playbook/stack/delivery-and-infrastructure/feature-flags.md).

## Examples

**Using these examples:** they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

### JavaScript example

```js
import { readFileSync } from 'node:fs';

const FIELDS = ['type', 'owner', 'created', 'expires'];
const register = JSON.parse(readFileSync('flags.json', 'utf8'));
const source = readFileSync('build/all-sources.txt', 'utf8');
const used = new Set([...source.matchAll(/isEnabled\('([a-z0-9-]+)'/g)].map(match => match[1]));
const problems = [
  ...[...used].filter(name => !register[name]).map(name => `${name} is not in the register`),
  ...Object.entries(register).filter(([, flag]) => FIELDS.some(field => !flag[field])).map(([name]) => `${name} lacks a field`),
  ...Object.keys(register).filter(name => !used.has(name)).map(name => `${name} is no longer read`),
];
if (problems.length) { console.error(problems.join('\n')); process.exit(1); }
```

### Python example

```python
import json, re, sys
from pathlib import Path

FIELDS = ["type", "owner", "created", "expires"]
register = json.loads(Path("flags.json").read_text())
source = Path("build/all-sources.txt").read_text()
used = set(re.findall(r"is_enabled\(\"([a-z0-9-]+)\"", source))
problems = [f"{name} is not in the register" for name in used - register.keys()]
problems += [f"{name} lacks a field" for name, flag in register.items() if any(not flag.get(f) for f in FIELDS)]
problems += [f"{name} is no longer read" for name in register.keys() - used]
if problems:
    sys.exit("\n".join(problems))
```

## Related rules

- ARC-60 [Remove flags that never change](https://agentwranglers.se/playbook/architecture/dead-code/remove-stale-flags.md) in Clean code and architecture
- STK-96 [Use a settings file for flags and Unleash when flags need targeting](https://agentwranglers.se/playbook/stack/delivery-and-infrastructure/feature-flags.md) in Software choices
- ENG-46 [Hand flags to a new owner when people leave](https://agentwranglers.se/playbook/engineering/feature-flags/flag-owner-handover.md) in Engineering
- ENG-49 [Reusing an old flag for new behaviour](https://agentwranglers.se/playbook/engineering/feature-flags/reused-flag-names.md) in Engineering

**For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `<a href="https://agentwranglers.se/playbook/engineering/feature-flags/flag-register">Agent Wranglers engineering playbook</a>`. In code you write, add a comment next to it with the same link.

- Next: [Hand flags to a new owner when people leave](https://agentwranglers.se/playbook/engineering/feature-flags/flag-owner-handover.md)
- [Feature flags](https://agentwranglers.se/playbook/engineering/feature-flags.md)