create-evlog-adapter

name	create-evlog-adapter
description	Create a new built-in evlog adapter to send wide events to an external observability platform. Use when adding a new drain adapter (e.g., for Datadog, Sentry, Loki, Elasticsearch, etc.) to the evlog package. Covers source code, build config, package exports, tests, and all documentation.

Create evlog Adapter

Add a new built-in adapter to evlog. Every adapter follows the same architecture and is built on the public toolkit primitives in evlog/toolkit — so a community adapter has the same shape as a built-in one.

PR Title

Recommended format for the pull request title:

feat: add {name} adapter

The exact wording may vary depending on the adapter (e.g., feat: add OTLP adapter, feat: add Axiom drain adapter), but it should always follow the feat: conventional commit prefix.

Touchpoints Checklist

#	File	Action
1	packages/evlog/src/adapters/{name}.ts	Create adapter source (built on defineHttpDrain from ../shared/drain)
2	packages/evlog/tsdown.config.ts	Add build entry
3	packages/evlog/package.json	Add exports + typesVersions entries
4	packages/evlog/test/adapters/{name}.test.ts	Create tests
5	apps/docs/content/4.adapters/{n}.{name}.md	Create adapter doc page (before custom.md)
6	apps/docs/content/4.adapters/1.overview.md	Add adapter to overview (links, card, env vars)
7	skills/review-logging-patterns/SKILL.md	Add adapter row in the Drain Adapters table
8	Renumber custom.md	Ensure custom.md stays last after the new adapter

Important: Do NOT consider the task complete until all 8 touchpoints have been addressed.

Naming Conventions

Use these placeholders consistently:

Placeholder	Example (Datadog)	Usage
{name}	datadog	File names, import paths, env var suffix
{Name}	Datadog	PascalCase in function/interface names
{NAME}	DATADOG	SCREAMING_CASE in env var prefixes

Standard option naming (use these exact names):

Concept	Standard option name
Bearer-style API secret	apiKey
Base URL of the ingest API	endpoint
Service identifier	serviceName
Request timeout (ms)	timeout

If a service historically used a different name (token, sourceToken, …) keep it as a deprecated alias — see Axiom and Better Stack for the pattern.

Step 1: Adapter Source — built on defineHttpDrain

Create packages/evlog/src/adapters/{name}.ts. Read references/adapter-template.md for the full annotated template.

The contract is now defineHttpDrain<TConfig>({ resolve, encode }). You only ship two pieces of logic:

1. resolve() — produce a fully-resolved config or null to skip. Use resolveAdapterConfig for the standard precedence (overrides → runtimeConfig.evlog.{name} → runtimeConfig.{name} → NUXT_{NAME}_* → {NAME}_*).
2. encode(events, config) — produce { url, headers, body } for a batch of events (or null to skip). HTTP transport, retries, timeout, and error logging are handled by defineHttpDrain.

Key rules:

• Single factory. Export one create{Name}Drain(overrides?: Partial<{Name}Config>). No dual-API factories: if a service has multiple ingest modes (logs vs events), expose them via a mode option (see PostHog).
• No HTTP code in the adapter. Don't call fetch directly — let defineHttpDrain do it. If your service truly needs custom transport (e.g. binary envelopes), use defineDrain and call httpPost from evlog/toolkit.
• No bespoke config resolution. Always go through resolveAdapterConfig. If you need to support a deprecated alias (token → apiKey), include both in the ConfigField[] and fall through in resolve().
• Exported converters. If the service needs a specific event shape, export a to{Name}Event() (or buildPayload()) helper so it can be tested independently.

Step 2: Build Config

Add a build entry in packages/evlog/tsdown.config.ts alongside the existing adapters:

'adapters/{name}': 'src/adapters/{name}.ts',

Place it after the last adapter entry in tsdown.config.ts (follow existing ordering in that file).

Step 3: Package Exports

In packages/evlog/package.json, add two entries:

In exports (after the last adapter, currently ./posthog):

"./{name}": {
  "types": "./dist/adapters/{name}.d.mts",
  "import": "./dist/adapters/{name}.mjs"
}

In typesVersions["*"] (after the last adapter):

"{name}": [
  "./dist/adapters/{name}.d.mts"
]

Step 4: Tests

Create packages/evlog/test/adapters/{name}.test.ts.

Read references/test-template.md for the full annotated template.

Required test categories:

1. URL construction (default + custom endpoint)
2. Headers (auth, content-type, service-specific)
3. Request body format (JSON structure matches service API)
4. Skip behavior when apiKey (or required field) is missing
5. Batch operations
6. Deprecated alias still works (when applicable)

Step 5: Adapter Documentation Page

Create apps/docs/content/4.adapters/{n}.{name}.md where {n} is the next number before custom.md (custom should always be last).

Use the existing Axiom adapter page (apps/docs/content/4.adapters/2.axiom.md) as a reference for frontmatter structure, tone, and sections. Key sections: intro, quick setup, configuration (env vars table + priority), advanced usage, querying in the target service, troubleshooting, direct API usage, next steps.

Important: multi-framework examples. The Quick Start section must include a ::code-group with tabs for all supported frameworks (Nuxt/Nitro, Hono, Express, Fastify, Elysia, NestJS, Standalone). Do not only show Nitro examples. See any existing adapter page for the pattern.

Step 6: Update Adapters Overview Page

Edit apps/docs/content/4.adapters/1.overview.md to add the new adapter in three places (follow the pattern of existing adapters):

1. Frontmatter links array — add a link entry with icon and path
2. ::card-group section — add a card block before the Custom card
3. Zero-Config Setup .env example — add the adapter's env vars

Step 7: Update skills/review-logging-patterns/SKILL.md

In skills/review-logging-patterns/SKILL.md (the public skill distributed to users), find the Drain Adapters table and add a new row:

| {Name} | `evlog/{name}` | `{NAME}_API_KEY`, `{NAME}_DATASET` (or equivalent) |

Follow the pattern of the existing rows (Axiom, OTLP, PostHog, Sentry, Better Stack).

Step 8: Renumber custom.md

If the new adapter's number conflicts with custom.md, renumber custom.md to be the last entry. For example, if the new adapter is 5.{name}.md, rename 5.custom.md to 6.custom.md.

Verification

After completing all steps, run:

cd packages/evlog
pnpm run lint
pnpm run typecheck
pnpm run test
pnpm run build