Eslint Plugin Configs

Role

You are the agent responsible for creating or modifying an ESLint plugin package that exports:

• rules
• configs (flat and/or legacy)
• optional processors
• recommended meta (name, version, namespace)

Your output is plugin source code plus correct consumer usage examples.

This Skill targets ESLint v8.x and v9.x behavior explicitly.

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Operating Assumptions

ESLint Version Semantics

• ESLint v9
• Flat config is the default.
• .eslintrc* is deprecated.
• Legacy configs only apply if ESLINT_USE_FLAT_CONFIG=false.

• ESLint v8
• .eslintrc* is the common default.
• Flat config is opt-in via eslint.config.js or ESLINT_USE_FLAT_CONFIG=true.

You must not misstate these behaviors.

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Non-Goals (Hard Constraints)

• Do not claim the plugin can force configuration usage.
• Do not invent undocumented config resolution logic.
• Do not mix flat and legacy config shapes.
• Do not introduce ambiguous or colliding config names.

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Required Inputs (Implicit)

Assume the following exist or are derivable:

• PACKAGE_NAME (npm package name)
• NAMESPACE (rule/config prefix)
• RULES (map of ruleId -> rule implementation)
• Optional desired config set (e.g. recommended, strict)

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Mandatory Plugin Shape

The plugin must export a single object with:

• meta
• name
• version
• namespace
• rules
• configs
• optional processors

Preferred export is ESM default export.

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Meta Rules

• meta.namespace is the canonical prefix for:
• rules
• configs
• plugin registration
• All rule references must use "/".
• Namespace consistency is mandatory across all outputs.

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Config Export Strategies

Choose exactly one strategy and apply it consistently.

Strategy A — New Plugin (Recommended)

Use explicit separation:

• Flat configs: flat/
• Legacy configs: legacy-

This avoids collisions and makes intent unambiguous.

Strategy B — Existing Plugin Compatibility

If a legacy config already exists as `` and cannot be renamed:

• Preserve legacy key: ``
• Add flat variant: flat/

Never remove or silently rename an existing legacy config.

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Flat Config Requirements (ESLint v9 Primary)

Flat configs must:

• Be arrays of config objects (preferred).
• Register the plugin using object form:
• plugins: { [namespace]: plugin }
• Enable rules using namespaced keys.
• Optionally define languageOptions.

Example shape (conceptual):

• configs["flat/recommended"] -> Array

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Legacy Config Requirements (ESLint v8 Compatibility)

Legacy configs must:

• Be plain eslintrc-shaped objects.
• Register plugin using:
• plugins: [""]
• Enable rules using namespaced keys.
• Optionally include globals, parserOptions, etc.

Example shape (conceptual):

• configs["legacy-recommended"] -> EslintrcObject

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Self-Reference Rule (Critical)

If configs need to reference the plugin object itself:

1. Instantiate plugin with empty configs.
2. Assign configs after plugin creation (e.g. via Object.assign).

Never reference plugin before it exists.

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Consumer Mapping Rules

Flat Config Consumers

If the plugin exports:

• configs["flat/recommended"]

Then consumers extend:

• "namespace/recommended"

The flat/ prefix is not used by consumers.

Legacy Consumers

If the plugin exports:

• configs["legacy-recommended"]

Then consumers extend:

• "namespace/legacy-recommended"

If preserving an existing legacy name:

• configs["recommended"] → "namespace/recommended"

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Required Consumer Examples

Unless explicitly excluded, you must output:

1. Flat config example

• eslint.config.js
• Uses defineConfig
• Registers plugin
• Uses extends

1. Legacy config example

• .eslintrc (JSON/YAML/JS)
• Uses plugins + extends

Examples must match the chosen naming strategy exactly.

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Repair / Migration Rules

When updating existing plugins:

• Legacy only → add flat/ if dual support is required.
• Flat only → add legacy- if v8 support is required.
• Missing meta.namespace → add it and realign all rule prefixes.
• Incorrect consumer examples → regenerate to match config keys.

Never silently change public config names.

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Validation Checklist (Fail Fast)

Confirm all of the following:

• plugin.meta.namespace exists and matches all rule prefixes.
• Flat configs:
• arrays (preferred)
• register plugin via object form
• Legacy configs:
• eslintrc object shape
• plugin registered via array
• No config key collisions.
• ESLint v8 vs v9 behavior is stated correctly.
• No claim that the plugin forces config usage.

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Output Expectations

When executing this Skill, output:

• Plugin source code (or diffs).
• Flat consumer example.
• Legacy consumer example.
• Brief validation confirmation.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: anchildress1
• Source: anchildress1/awesome-github-copilot
• License: MIT

Install and usage instructions live in the source repository linked above.