How we fit together

Faultlines + Sourcegraph

Name: Faultlines
Author: Faultlines

Sourcegraph indexes massive codebases for search and intelligence at scale. Faultlines abstracts those files into features and flows. Different abstraction layers; both can run together, or Faultlines alone if your codebase fits in one repo.

What Sourcegraph does best

The best code-search tool ever built. Cross-reference across hundreds of repositories, batch changes, code ownership, mature at huge-monorepo scale. In 2025 they moved Enterprise-only with Amp AI — they now serve large orgs needing search at scale.

Code search across hundreds of repositories
Code intelligence + cross-reference
Batch changes across repos
Code ownership at scale
Mature at 100+ repo / huge-monorepo scale

What Faultlines adds

A higher-abstraction layer over code. Sourcegraph indexes every file; Faultlines groups files into features and surfaces business-level context. Sourcegraph’s audience moved enterprise; Faultlines covers the small-to-mid SaaS segment.

Feature + flow map of the codebase
Hotspots, churn, ownership per feature
Sentry + PostHog attribution per feature
MCP server for Cursor, Claude Code, Cline, Aider
Open-source CLI, free for public repos forever

Using both

How they actually combine

Engineer asks Sourcegraph: “find every usage of chargeCustomer across our 50 repos.”

Sourcegraph returns 47 call sites with full cross-reference and symbol intelligence.

Faultlines tells you which features those 47 sites belong to: 32 in Billing, 8 in Reports, 7 in shared utility — and that Billing had 47 errors last week. The refactor scope just clarified itself.

Or alone

Just Faultlines, on its own

Faultlines isn’t a code-search engine. For “where is this symbol referenced across 50 repos?” you want Sourcegraph (or GitHub code search). For “what feature is this function part of, and what’s its health?” you want Faultlines. If your codebase fits in one repo and is under 1.5M LOC, Faultlines alone covers most search-style questions through its MCP server. If you’re a 100-repo enterprise, Sourcegraph plus Faultlines is the natural pairing.

Side by side

Where each one focuses

Focus area	Sourcegraph	Faultlines
Primary unit	File + symbol index	Feature + flow map
Cross-repo search	✓ best-in-class	—
Symbol intelligence	✓	via MCP
Behavioural analysis (hotspots)	—	✓
Runtime signal	—	Sentry + PostHog
Pricing	$59/dev Enterprise-only	$19–299/org
Best fit	100+ repo monorepo / multi-repo	3–50 dev SaaS teams

Honest take

No vendor pressure

Sourcegraph is the best code-search tool ever built. They explicitly moved upmarket in 2025 — small / mid SaaS teams aren’t their priority anymore. Faultlines covers that abandoned segment with a different abstraction layer (features instead of files). Huge org with cross-repo search needs →Sourcegraph . SaaS team that wants AI-agent context + feature-level intelligence → Faultlines. Both? Run them together.

Also comparing

Other tools we work alongside