/kfl

name: kfl
user-invocable: false
description: >
  KFL2 (Kubeshark Filter Language) reference. This skill MUST be loaded before
  writing, constructing, or suggesting any KFL filter expression. KFL is statically
  typed — incorrect field names or syntax will fail silently or error. Do not guess
  at KFL syntax without this skill loaded. Trigger on any mention of KFL, CEL filters,
  traffic filtering, display filters, query syntax, filter expressions, write a filter,
  construct a query, build a KFL, create a filter expression, "how do I filter",
  "show me only", "find traffic where", protocol-specific queries (HTTP status codes,
  DNS lookups, Redis commands, Kafka topics), Kubernetes-aware filtering (by namespace,
  pod, service, label, annotation), L4 connection/flow filters, time-based queries,
  or any request to slice/search/narrow network traffic in Kubeshark. Also trigger
  when other skills need to construct filters — KFL is the query language for all
  Kubeshark traffic analysis.
last-updated: 2026-05-08

KFL2 — Kubeshark Filter Language

You are a KFL2 expert. KFL2 is built on Google's CEL (Common Expression Language) and is the query language for all Kubeshark traffic analysis. It operates as a **display filter** — it doesn't affect what's captured, only what you see.

Think of KFL the way you think of SQL for databases or Google search syntax for the web. Kubeshark captures and indexes all cluster traffic; KFL is how you search it.

For the complete variable and field reference, see `references/kfl2-reference.md`.

Core Syntax

KFL expressions are boolean CEL expressions. An empty filter matches everything.

Operators

| Category | Operators | |----------|-----------| | Comparison | `==`, `!=`, `<`, `<=`, `>`, `>=` | | Logical | `&&`, `\|\|`, `!` | | Arithmetic | `+`, `-`, `*`, `/`, `%` | | Membership | `in` | | Ternary | `condition ? true_val : false_val` |

String Functions

str.contains(substring)      // Substring search
str.startsWith(prefix)       // Prefix match
str.endsWith(suffix)         // Suffix match
str.matches(regex)           // Regex match
size(str)                    // String length

Collection Functions

size(collection)             // List/map/string length
key in map                   // Key existence
map[key]                     // Value access
map_get(map, key, default)   // Safe access with default
value in list                // List membership

Time Functions

timestamp("2026-03-14T22:00:00Z")   // Parse ISO timestamp
duration("5m")                        // Parse duration
now()                                 // Current time (snapshot at filter creation)

Negation

!http                                // Everything that is NOT HTTP
http && status_code != 200           // HTTP responses that aren't 200
http && !path.contains("/health")    // Exclude health checks
!(src.pod.namespace == "kube-system")  // Exclude system namespace

Protocol Detection

Boolean flags that indicate which protocol was detected. Use these as the first filter term — they're fast and narrow the search space immediately.

| Flag | Protocol | Flag | Protocol | |------|----------|------|----------| | `http` | HTTP/1.1, HTTP/2 | `redis` | Redis | | `dns` | DNS | `kafka` | Kafka | | `tls` | eBPF TLS interception | `amqp` | AMQP | | `tcp` | TCP | `ldap` | LDAP | | `udp` | UDP | `ws` | WebSocket | | `sctp` | SCTP | `gql` | GraphQL (v1+v2) | | `icmp` | ICMP | `gqlv1` / `gqlv2` | GraphQL version-specific | | `grpc` | gRPC (HTTP/2 sub-protocol) | `mongodb` | MongoDB | | `mysql` | MySQL | `postgresql` | PostgreSQL | | `radius` | RADIUS | | | | `diameter` | Diameter | `conn` / `flow` | L4 connection/flow tracking | | | | `tcp_conn` / `udp_conn` | Transport-specific connections |

Kubernetes Context

The most common starting point. Filter by where traffic originates or terminates.

Pod and Service Fields

src.pod.name == "orders-594487879c-7ddxf"
dst.pod.namespace == "production"
src.service.name == "api-gateway"
dst.service.namespace == "payments"

Pod fields fall back to service data when pod info is unavailable, so `dst.pod.namespace` works even for service-level entries.

Summary Name and Namespace

Convenience variables that pick the best available identity for a peer:

src.name == "api-gateway"                    // pod > service > dns > process
dst.name.contains("payment")                 // works across identity types
src.namespace == "production"                 // pod namespace, falls back to service
dst.namespace != "kube-system"               // exclude system namespace

Aggregate Collections

Match against any direction (src or dst):

"production" in namespaces           // Any namespace match
"orders" in pods                     // Any pod name match
"api-gateway" in services            // Any service name match

Labels and Annotations

map_get(local_labels, "app", "") == "checkout"   // Safe access with default
map_get(remote_labels, "version", "") == "canary"
"tier" in local_labels                            // Label existence check

Always use `map_get()` for labels and annotations — direct access like `local_labels["app"]` errors if the key doesn't exist.

Node and Process

node_name == "ip-10-0-25-170.ec2.internal"
local_process_name == "nginx"
remote_process_name.contains("postgres")

DNS Resolution

src.dns == "api.example.com"
dst.dns.contains("redis")

HTTP Filtering

HTTP is the most common protocol for API-level investigation.

Fields

| Field | Type | Example | |-------|------|---------| | `method` | string | `"GET"`, `"POST"`, `"PUT"`, `"DELETE"` | | `url` | string | Full path + query: `"/api/users?id=123"` | | `path` | string | Path only: `"/api/users"` | | `status_code` | int | `200`, `404`, `500` | | `http_version` | string | `"HTTP/1.1"`, `"HTTP/2"` | | `request.headers` | map | `request.headers["content-type"]