Logs

Log Drains Reference

Log Drains forward logs from your deployments to external endpoints for storage and analysis. To enable Log Drains, you must provide an endpoint URL to send the logs to. This URL can be a custom endpoint of yours or one provided by a third-party provider like Datadog, New Relic, or other observability services.

Vercel sends logs to endpoint URLs over HTTPS every time your deployments generate logs. Multiple logs may be batched into a single request when possible to optimize delivery performance.

Logs Schema

The following table describes the possible fields that are sent via Log Drains:

Name	Type	Required	Description	Example
`id`	string	Yes	Unique identifier for the log entry	`1573817187330377061717300000`
`deploymentId`	string	Yes	Identifier for the Vercel deployment	`dpl_233NRGRjVZX1caZrXWtz5g1TAksD`
`source`	enum	Yes	Origin of the log	`build`, `edge`, `lambda`, `static`, `external`, or `firewall`
`host`	string	Yes	Deployment unique URL hostname	`*.vercel.app`
`timestamp`	number	Yes	Unix timestamp when the log was generated	1573817187330
`projectId`	string	Yes	Identifier for the Vercel project	`gdufoJxB6b9b1fEqr1jUtFkyavUU`
`level`	enum	Yes	Log severity level	`info`, `warning`, `error`, or `fatal`
`message`	string	No	Log message content (may be truncated if over 256 KB)	`Adding customer to database...`
`buildId`	string	No	Identifier for the Vercel build	`bld_cotnkcr76` (only present on build logs)
`entrypoint`	string	No	Entrypoint for the request	`api/index.js`
`destination`	string	No	Origin of the external content	`https://vitals.vercel-insights.com/v1` (only on external logs)
`path`	string	No	Function or dynamic path of the request	`/dynamic/[route].json`
`type`	string	No	Log output type	`command`, `stdout`, `stderr`, `exit`, `deployment-state`, `delimiter`, `middleware`, `middleware-invocation`, `edge-function-invocation`, `metric`, `report`, `fatal`
`statusCode`	number	No	HTTP status code of the request	200 (`-1` means no response returned and the lambda crashed)
`requestId`	string	No	Identifier of the request	`643af4e3-975a-4cc7-9e7a-1eda11539d90`
`environment`	enum	No	Deployment environment	`production` or `preview`
`branch`	string	No	Git branch name	`main`
`ja3Digest`	string	No	JA3 fingerprint digest	`769c83e5b...`
`ja4Digest`	string	No	JA4 fingerprint digest	`t13d1516h2...`
`edgeType`	enum	No	Type of edge runtime	`edge-function` or `middleware`
`projectName`	string	No	Name of the Vercel project	`my-app`
`executionRegion`	string	No	Region where the request is executed	`sfo1`
`traceId`	string	No	Trace identifier for distributed tracing	`1b02cd14bb8642fd092bc23f54c7ffcd`
`spanId`	string	No	Span identifier for distributed tracing	`f24e8631bd11faa7`
`trace.id`	string	No	Trace	`1b02cd14bb8642fd092bc23f54c7ffcd`
`span.id`	string	No	Span	`f24e8631bd11faa7`
`proxy`	object	No	Contains information about proxy requests	See proxy fields below
`proxy.timestamp`	number	Yes*	Unix timestamp when the proxy request was made	1573817250172
`proxy.method`	string	Yes*	HTTP method of the request	`GET`
`proxy.host`	string	Yes*	Hostname of the request	`test.vercel.app`
`proxy.path`	string	Yes*	Request path with query parameters	`/dynamic/some-value.json?route=some-value`
`proxy.userAgent`	array	Yes*	User agent strings of the request	`["Mozilla/5.0..."]`
`proxy.referer`	string	Yes*	Referer of the request	`*.vercel.app`
`proxy.region`	string	Yes*	Region where the request is processed	`sfo1`
`proxy.statusCode`	number	No	HTTP status code of the proxy request	200 (`-1` means revalidation occurred in the background)
`proxy.clientIp`	string	No	Client IP address	`120.75.16.101`
`proxy.scheme`	string	No	Protocol of the request	`https`
`proxy.responseByteSize`	number	No	Size of the response in bytes	1024
`proxy.cacheId`	string	No	Original request ID when request is served from cache	`pdx1::v8g4b-1744143786684-93dafbc0f70d`
`proxy.pathType`	string	No	How the request was served based on its path and project configuration	`func`, `prerender`, `background_func`, `edge`, `middleware`, `streaming_func`, `partial_prerender`, `external`, `static`, `not_found`, `unknown`, `api`
`proxy.pathTypeVariant`	string	No	Variant of the path type	`api`
`proxy.vercelId`	string	No	Vercel-specific identifier	`sfo1::abc123`
`proxy.vercelCache`	enum	No	Cache status sent to the browser	`MISS`, `HIT`, `STALE`, `BYPASS`, `PRERENDER`, `REVALIDATED`
`proxy.lambdaRegion`	string	No	Region where lambda function executed	`sfo1`
`proxy.wafAction`	enum	No	Action taken by firewall rules	`log`, `challenge`, `deny`, `bypass`, `rate_limit`
`proxy.wafRuleId`	string	No	ID of the firewall rule that matched	`rule_gAHz8jtSB1Gy`

*Required when proxy object is present

Format

Vercel supports the following formats for Log Drains. You can configure the format when configuring the Drain destination:

JSON

Vercel sends logs as JSON arrays containing log objects:

{ "id": "1573817187330377061717300000", "deploymentId": "dpl_233NRGRjVZX1caZrXWtz5g1TAksD", "source": "build", "host": "my-app-abc123.vercel.app", "timestamp": 1573817187330, "projectId": "gdufoJxB6b9b1fEqr1jUtFkyavUU", "level": "info", "message": "Build completed successfully", "buildId": "bld_cotnkcr76", "type": "stdout", "projectName": "my-app" }
{ "id": "1573817250283254651097202070", "deploymentId": "dpl_233NRGRjVZX1caZrXWtz5g1TAksD", "source": "lambda", "host": "my-app-abc123.vercel.app", "timestamp": 1573817250283, "projectId": "gdufoJxB6b9b1fEqr1jUtFkyavUU", "level": "info", "message": "API request processed", "entrypoint": "api/index.js", "requestId": "643af4e3-975a-4cc7-9e7a-1eda11539d90", "statusCode": 200, "path": "/api/users", "executionRegion": "sfo1", "environment": "production", "traceId": "1b02cd14bb8642fd092bc23f54c7ffcd", "spanId": "f24e8631bd11faa7", "trace.id": "1b02cd14bb8642fd092bc23f54c7ffcd", "span.id": "f24e8631bd11faa7", "proxy": { "timestamp": 1573817250172, "method": "GET", "host": "my-app.vercel.app", "path": "/api/users?page=1", "userAgent": ["Mozilla/5.0..."], "referer": "https://my-app.vercel.app", "region": "sfo1", "statusCode": 200, "clientIp": "120.75.16.101", "scheme": "https", "vercelCache": "MISS" } }

NDJSON

Vercel sends logs as newline-delimited JSON objects:

{"id": "1573817187330377061717300000","deploymentId": "dpl_233NRGRjVZX1caZrXWtz5g1TAksD","source": "build","host": "my-app-abc123.vercel.app","timestamp": 1573817187330,"projectId": "gdufoJxB6b9b1fEqr1jUtFkyavUU","level": "info","message": "Build completed successfully","buildId": "bld_cotnkcr76","type": "stdout","projectName": "my-app"}
{"id": "1573817250283254651097202070","deploymentId": "dpl_233NRGRjVZX1caZrXWtz5g1TAksD","source": "lambda","host": "my-app-abc123.vercel.app","timestamp": 1573817250283,"projectId": "gdufoJxB6b9b1fEqr1jUtFkyavUU","level": "info","message": "API request processed","entrypoint": "api/index.js","requestId": "643af4e3-975a-4cc7-9e7a-1eda11539d90","statusCode": 200,"path": "/api/users","executionRegion": "sfo1","environment": "production","traceId": "1b02cd14bb8642fd092bc23f54c7ffcd","spanId": "f24e8631bd11faa7","trace.id": "1b02cd14bb8642fd092bc23f54c7ffcd","span.id": "f24e8631bd11faa7","proxy": {"timestamp": 1573817250172,"method": "GET","host": "my-app.vercel.app","path": "/api/users?page=1","userAgent": ["Mozilla/5.0..."],"referer": "https://my-app.vercel.app","region": "sfo1","statusCode": 200,"clientIp": "120.75.16.101","scheme": "https","vercelCache": "MISS"}}

Log Sources

When you configure a Log Drain in the Vercel UI, you can set which sources to receive logs from:

value	Details
`static`	Requests to static assets like HTML and CSS files
`lambda`	Output from Vercel Functions like API Routes
`edge`	Output from Vercel Functions using Edge runtime
`build`	Output from the Build Step
`external`	External rewrites to a different domain
`firewall`	Outputs log data from requests denied by Vercel Firewall rules

Log Environments

When you configure a Log Drain in the Vercel UI, you can set which environments to receive logs from:

value	Details
`production`	Logs from production deployments with assigned domain(s)
`preview`	Logs from deployments accessed through the generated deployment URL

Sampling Rate

When you configure a Log Drain in the Vercel UI, you can set the sampling rate to control the volume of data sent. This helps manage costs when you have high traffic volumes.

More resources

For more information on Log Drains and how to use them, check out the following resources:

Using Drains

Traces

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