ASP.NET Core built-in metrics

This article describes the metrics built-in for ASP.NET Core produced using the System.Diagnostics.Metrics API. For a listing of metrics based on the older EventCounters API, see Available counters.

Tip

For more information about how to collect, report, enrich, and test ASP.NET Core metrics, see Using ASP.NET Core metrics.

Microsoft.AspNetCore.Hosting

The Microsoft.AspNetCore.Hosting metrics report high-level information about HTTP requests received by ASP.NET Core:

• http.server.request.duration
• http.server.active_requests

Metric: http.server.request.duration

Name	Instrument Type	Unit (UCUM)	Description
http.server.request.duration	Histogram	s	Measures the duration of inbound HTTP requests.

Attribute	Type	Description	Examples	Presence
http.route	string	The matched route.	{controller}/{action}/{id?}	If it's available.
error.type	string	Describes a class of error the operation ended with.	timeout; name_resolution_error; 500	If request has ended with an error.
http.request.method	string	HTTP request method.	GET; POST; HEAD	Always
http.response.status_code	int	HTTP response status code.	200	If one was sent.
network.protocol.version	string	Version of the protocol specified in network.protocol.name.	3.1.1	Always
url.scheme	string	The URI scheme component identifying the used protocol.	http; https	Always
aspnetcore.request.is_unhandled	Boolean	True when the request wasn't handled by the application pipeline.	true	If the request was unhandled.

The time used to handle an inbound HTTP request as measured at the hosting layer of ASP.NET Core. The time measurement starts once the underlying web host has:

• Sufficiently parsed the HTTP request headers on the inbound network stream to identify the new request.
• Initialized the context data structures such as the HttpContext.

The time ends when:

• The ASP.NET Core handler pipeline is finished executing.
• All response data has been sent.
• The context data structures for the request are being disposed.

When using OpenTelemetry, the default buckets for this metric are set to [ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ].

Metric: http.server.active_requests

Name	Instrument Type	Unit (UCUM)	Description
http.server.active_requests	UpDownCounter	{request}	Measures the number of concurrent HTTP requests that are currently in-flight.

Attribute	Type	Description	Examples	Presence
http.request.method	string	HTTP request method. [1]	GET; POST; HEAD	Always
url.scheme	string	The URI scheme component identifying the used protocol.	http; https	Always

Microsoft.AspNetCore.Routing

The Microsoft.AspNetCore.Routing metrics report information about routing HTTP requests to ASP.NET Core endpoints:

• aspnetcore.routing.match_attempts

Metric: aspnetcore.routing.match_attempts

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.routing.match_attempts	Counter	{match_attempt}	Number of requests that were attempted to be matched to an endpoint.

Attribute	Type	Description	Examples	Presence
aspnetcore.routing.match_status	string	Match result	success; failure	Always
aspnetcore.routing.is_fallback_route	boolean	A value that indicates whether the matched route is a fallback route.	True	If a route was successfully matched.
http.route	string	The matched route	{controller}/{action}/{id?}	If a route was successfully matched.

Microsoft.AspNetCore.Diagnostics

The Microsoft.AspNetCore.Diagnostics metrics report diagnostics information from ASP.NET Core error handling middleware:

• aspnetcore.diagnostics.exceptions

Metric: aspnetcore.diagnostics.exceptions

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.diagnostics.exceptions	Counter	{exception}	Number of exceptions caught by exception handling middleware.

Attribute	Type	Description	Examples	Presence
aspnetcore.diagnostics.exception.result	string	ASP.NET Core exception middleware handling result	handled; unhandled	Always
aspnetcore.diagnostics.handler.type	string	Full type name of the IExceptionHandler implementation that handled the exception.	Contoso.MyHandler	If the exception was handled by this handler.
exception.type	string	The full name of exception type.	System.OperationCanceledException; Contoso.MyException	Always

Microsoft.AspNetCore.RateLimiting

The Microsoft.AspNetCore.RateLimiting metrics report rate limiting information from ASP.NET Core rate-limiting middleware:

• aspnetcore.rate_limiting.active_request_leases
• aspnetcore.rate_limiting.request_lease.duration
• aspnetcore.rate_limiting.queued_requests
• aspnetcore.rate_limiting.request.time_in_queue
• aspnetcore.rate_limiting.requests

Metric: aspnetcore.rate_limiting.active_request_leases

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.rate_limiting.active_request_leases	UpDownCounter	{request}	Number of requests that are currently active on the server that hold a rate limiting lease.

Attribute	Type	Description	Examples	Presence
aspnetcore.rate_limiting.policy	string	Rate limiting policy name.	fixed; sliding; token	If the matched endpoint for the request had a rate-limiting policy.

Metric: aspnetcore.rate_limiting.request_lease.duration

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.rate_limiting.request_lease.duration	Histogram	s	The duration of the rate limiting lease held by requests on the server.

Attribute	Type	Description	Examples	Presence
aspnetcore.rate_limiting.policy	string	Rate limiting policy name.	fixed; sliding; token	If the matched endpoint for the request had a rate-limiting policy.

Metric: aspnetcore.rate_limiting.queued_requests

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.rate_limiting.queued_requests	UpDownCounter	{request}	Number of requests that are currently queued waiting to acquire a rate limiting lease.

Attribute	Type	Description	Examples	Presence
aspnetcore.rate_limiting.policy	string	Rate limiting policy name.	fixed; sliding; token	If the matched endpoint for the request had a rate-limiting policy.

Metric: aspnetcore.rate_limiting.request.time_in_queue

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.rate_limiting.request.time_in_queue	Histogram	s	The time a request spent in a queue waiting to acquire a rate limiting lease.

Attribute	Type	Description	Examples	Presence
aspnetcore.rate_limiting.policy	string	Rate limiting policy name.	fixed; sliding; token	If the matched endpoint for the request had a rate-limiting policy.
aspnetcore.rate_limiting.result	string	The rate limiting result shows whether lease was acquired or contains a rejection reason.	acquired; request_canceled	Always

Metric: aspnetcore.rate_limiting.requests

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.rate_limiting.requests	Counter	{request}	Number of requests that tried to acquire a rate limiting lease.

Attribute	Type	Description	Examples	Presence
aspnetcore.rate_limiting.policy	string	Rate limiting policy name.	fixed; sliding; token	If the matched endpoint for the request had a rate-limiting policy.
aspnetcore.rate_limiting.result	string	The rate limiting result shows whether lease was acquired or contains a rejection reason.	acquired; request_canceled	Always

Microsoft.AspNetCore.HeaderParsing

The Microsoft.AspNetCore.HeaderParsing metrics report information about ASP.NET Core header parsing:

• aspnetcore.header_parsing.parse_errors
• aspnetcore.header_parsing.cache_accesses

Metric: aspnetcore.header_parsing.parse_errors

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.header_parsing.parse_errors	Counter	{parse_error}	Number of errors that occurred when parsing HTTP request headers.

Attribute	Type	Description	Examples	Presence
aspnetcore.header_parsing.header.name	string	The header name.	Content-Type	Always
error.type	string	The error message.	Unable to parse media type value.	Always

Metric: aspnetcore.header_parsing.cache_accesses

The metric is emitted only for HTTP request header parsers that support caching.

Name	Instrument Type	Unit (UCUM)	Description
aspnetcore.header_parsing.cache_accesses	Counter	{cache_access}	Number of times a cache storing parsed header values was accessed.

Attribute	Type	Description	Examples	Presence
aspnetcore.header_parsing.header.name	string	The header name.	Content-Type	Always
aspnetcore.header_parsing.cache_access.type	string	A value indicating whether the header's value was found in the cache or not.	Hit; Miss	Always

Microsoft.AspNetCore.Server.Kestrel

The Microsoft.AspNetCore.Server.Kestrel metrics report HTTP connection information from ASP.NET Core Kestrel web server:

• kestrel.active_connections
• kestrel.connection.duration
• kestrel.rejected_connections
• kestrel.queued_connections
• kestrel.queued_requests
• kestrel.upgraded_connections
• kestrel.tls_handshake.duration
• kestrel.active_tls_handshakes

Metric: kestrel.active_connections

Name	Instrument Type	Unit (UCUM)	Description
kestrel.active_connections	UpDownCounter	{connection}	Number of connections that are currently active on the server.

Attribute	Type	Description	Examples	Presence
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

Metric: kestrel.connection.duration

Name	Instrument Type	Unit (UCUM)	Description
kestrel.connection.duration	Histogram	s	The duration of connections on the server.

Attribute	Type	Description	Examples	Presence
error.type	string	Describes a type of error the connection ended with, or the unhandled exception type thrown during the connection pipeline. Known connection errors can be found at Semantic Conventions for Kestrel web server metrics.	connection_reset; invalid_request_headers; System.OperationCanceledException	If the connection ended with a known error or an exception was thrown.
network.protocol.name	string	OSI application layer or non-OSI equivalent.	http; web_sockets	Always
network.protocol.version	string	Version of the protocol specified in network.protocol.name.	1.1; 2	Always
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.
tls.protocol.version	string	TLS protocol version.	1.2; 1.3	If the connection is secured with TLS.

As this metric is tracking the connection duration, and ideally http connections are used for multiple requests, the buckets should be longer than those used for request durations. For example, using [ 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300] provides an upper bucket of 5 mins.

When a connection ends with a known error, the error.type attribute value is set to the known error type. Known connection errors can be found at Semantic Conventions for Kestrel web server metrics.

Metric: kestrel.rejected_connections

Name	Instrument Type	Unit (UCUM)	Description
kestrel.rejected_connections	Counter	{connection}	Number of connections rejected by the server.

Attribute	Type	Description	Examples	Presence
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

Connections are rejected when the currently active count exceeds the value configured with MaxConcurrentConnections.

Metric: kestrel.queued_connections

Name	Instrument Type	Unit (UCUM)	Description
kestrel.queued_connections	UpDownCounter	{connection}	Number of connections that are currently queued and are waiting to start.

Attribute	Type	Description	Examples	Presence
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

Metric: kestrel.queued_requests

Name	Instrument Type	Unit (UCUM)	Description
kestrel.queued_requests	UpDownCounter	{request}	Number of HTTP requests on multiplexed connections (HTTP/2 and HTTP/3) that are currently queued and are waiting to start.

Attribute	Type	Description	Examples	Presence
network.protocol.name	string	OSI application layer or non-OSI equivalent.	http; web_sockets	Always
network.protocol.version	string	Version of the protocol specified in network.protocol.name.	1.1; 2	Always
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

Metric: kestrel.upgraded_connections

Name	Instrument Type	Unit (UCUM)	Description
kestrel.upgraded_connections	UpDownCounter	{connection}	Number of connections that are currently upgraded (WebSockets).

Attribute	Type	Description	Examples	Presence
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

The counter only tracks HTTP/1.1 connections.

Metric: kestrel.tls_handshake.duration

Name	Instrument Type	Unit (UCUM)	Description
kestrel.tls_handshake.duration	Histogram	s	The duration of TLS handshakes on the server.

Attribute	Type	Description	Examples	Presence
error.type	string	The full name of exception type.	System.OperationCanceledException; Contoso.MyException	If an exception was thrown.
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.
tls.protocol.version	string	TLS protocol version.	1.2; 1.3	If the connection is secured with TLS.

When using OpenTelemetry, the default buckets for this metic are set to [ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ].

Metric: kestrel.active_tls_handshakes

Name	Instrument Type	Unit (UCUM)	Description
kestrel.active_tls_handshakes	UpDownCounter	{handshake}	Number of TLS handshakes that are currently in progress on the server.

Attribute	Type	Description	Examples	Presence
network.transport	string	OSI transport layer or inter-process communication method.	tcp; unix	Always
network.type	string	OSI network layer or non-OSI equivalent.	ipv4; ipv6	If the transport is tcp or udp.
server.address	string	Server address domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.	example.com	Always
server.port	int	Server port number	80; 8080; 443	If the transport is tcp or udp.

Microsoft.AspNetCore.Http.Connections

The Microsoft.AspNetCore.Http.Connections metrics report connection information from ASP.NET Core SignalR:

• signalr.server.connection.duration
• signalr.server.active_connections

Metric: signalr.server.connection.duration

Name	Instrument Type	Unit (UCUM)	Description
signalr.server.connection.duration	Histogram	s	The duration of connections on the server.

Attribute	Type	Description	Examples	Presence
signalr.connection.status	string	SignalR HTTP connection closure status.	app_shutdown; timeout	Always
signalr.transport	string	SignalR transport type	web_sockets; long_polling	Always

Value	Description
normal_closure	The connection was closed normally.
timeout	The connection was closed due to a timeout.
app_shutdown	The connection was closed because the app is shutting down.

signalr.transport is one of the following:

Value	Protocol
server_sent_events	server-sent events
long_polling	Long Polling
web_sockets	WebSocket

As this metric is tracking the connection duration, and ideally SignalR connections are durable, the buckets should be longer than those used for request durations. For example, using [0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300] provides an upper bucket of 5 mins.

Metric: signalr.server.active_connections

Name	Instrument Type	Unit (UCUM)	Description
signalr.server.active_connections	UpDownCounter	{connection}	Number of connections that are currently active on the server.

Attribute	Type	Description	Examples	Presence
signalr.connection.status	string	SignalR HTTP connection closure status.	app_shutdown; timeout	Always
signalr.transport	string	SignalR transport type	web_sockets; long_polling	Always