Subsystems

The Prometheus repository is one Go module split into many packages. Each package below has a focused responsibility and is consumed by cmd/prometheus/main.go. The names mirror the area prefixes used in PR titles (AGENTS.md).

Subsystem	Path	What it owns
TSDB	tsdb/	The local time series database: head, WAL, blocks, index, chunks, compaction.
PromQL	promql/	Lexer, yacc parser, AST, and the query engine.
Scrape	scrape/	Scrape manager, scrape pools, scrape loops; turns target groups into samples.
Discovery	discovery/, plugins/	Service discovery framework and ~25 individual SDs.
Rules	rules/	Recording- and alerting-rule manager and evaluator.
Notifier	notifier/	Alertmanager dispatch.
Storage	storage/	Storage and Appender interfaces, fanout, exemplar storage helpers.
Remote write/read	storage/remote/	Outbound remote write, inbound remote-write/OTLP receivers, remote read.
Web / HTTP API	web/	HTTP server, federation, embedded UI assets, the v1 API.
Config	config/	YAML schema for prometheus.yml, parsing, validation, reload.
Model	model/	Cross-cutting domain types: labels, histogram, exemplar, relabel, textparse.
Util	util/	Shared helpers: pools, compression, annotations, features registry, kahansum, logging.
Tracing	tracing/	OpenTelemetry tracing setup.
Template	template/	Go-template helpers used by alert templates.

The entries below list the smaller packages explicitly so nothing is silently missed.

Reference for smaller packages

Path	Purpose
prompb/	Generated protobuf for remote write/read. v1 in prompb/, v2 in prompb/io/....
schema/	Metric type / unit metadata helpers shared by ingestion paths.
documentation/	User docs (documentation/*.md), example configs, and the prometheus-mixin Jsonnet.
docs/	Auto-generated and curated user docs (CLI, configuration, querying).
compliance/	Separate Go module: Remote Write 1.0 spec compliance tests for senders.
internal/tools/	Pinned versions of internal Go tools (promu, goyacc, …).
web/ui/	The React UIs (Mantine 3.x and legacy 2.x) and the shared CodeMirror modules.

For a top-down view of how these fit together, see Architecture.