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LibreChat

Project Overview

LibreChat is a monorepo with the following key workspaces:

Workspace Language Side Dependency Purpose
/api JS (legacy) Backend packages/api, packages/data-schemas, packages/data-provider, @librechat/agents Express server — minimize changes here
/packages/api TypeScript Backend packages/data-schemas, packages/data-provider New backend code lives here (TS only, consumed by /api)
/packages/data-schemas TypeScript Backend packages/data-provider Database models/schemas, shareable across backend projects
/packages/data-provider TypeScript Shared — Shared API types, endpoints, data-service — used by both frontend and backend
/client TypeScript/React Frontend packages/data-provider, packages/client Frontend SPA
/packages/client TypeScript Frontend packages/data-provider Shared frontend utilities

The source code for @librechat/agents (major backend dependency, same team) lives at https://github.com/danny-avila/agents.

Workspace Boundaries

  • All new backend code must be TypeScript in /packages/api.
  • Keep /api changes to the absolute minimum (thin JS wrappers calling into /packages/api).
  • Database-specific shared logic goes in /packages/data-schemas.
  • Frontend/backend shared API logic (endpoints, types, data-service) goes in /packages/data-provider.
  • Build data-provider from project root: npm run build:data-provider.

Branching and Pull Requests

  • Branch off dev, and target dev with every pull request. All work lands on dev first.
  • main is the released branch. It is kept as a fast-forward of dev and synced as-is, so it is always an ancestor of dev — equal to it right after a sync, behind it otherwise. It never carries a commit that dev does not have.
  • Never open a backport pull request to main. Anything merged to dev reaches main at the next sync; a second pull request for the same change is redundant.
  • The repository's default branch is main, so gh pr create and the GitHub UI target it unless told otherwise — always pass --base dev explicitly.
  • Pull requests opened against main are retargeted to dev automatically by .github/workflows/pr-retarget-dev.yml. The target: main label exempts one, as do release-bound upstream branches (dev, release/*, hotfix/*). Backport branches are deliberately not exempt — a backport merged straight to main is what breaks the fast-forward invariant.
  • Fixes #N does not close the issue. GitHub honors closing keywords only when a pull request merges into the default branch (main). Merging to dev does not close anything, and the later fast-forward of main is not a merge event either — close linked issues by hand.
  • Git worktrees share one stash stack. refs/stash lives in the common .git directory, so a bare git stash pop in one worktree can take work stashed in another. Prefer a throwaway WIP commit; if you must stash, git stash push -m <tag> and apply that specific entry.

Code Style

Naming and File Organization

  • Single-word file names whenever possible (e.g., permissions.ts, capabilities.ts, service.ts).
  • When multiple words are needed, prefer grouping related modules under a single-word directory rather than using multi-word file names (e.g., admin/capabilities.ts not adminCapabilities.ts).
  • The directory already provides context — app/service.ts not app/appConfigService.ts.

Structure and Clarity

  • Never-nesting: early returns, flat code, minimal indentation. Break complex operations into well-named helpers.
  • Functional first: pure functions, immutable data, map/filter/reduce over imperative loops. Only reach for OOP when it clearly improves domain modeling or state encapsulation.
  • No dynamic imports unless absolutely necessary.

DRY

  • Extract repeated logic into utility functions.
  • Reusable hooks / higher-order components for UI patterns.
  • Parameterized helpers instead of near-duplicate functions.
  • Constants for repeated values; configuration objects over duplicated init code.
  • Shared validators, centralized error handling, single source of truth for business rules.
  • Shared typing system with interfaces/types extending common base definitions.
  • Abstraction layers for external API interactions.

Iteration and Performance

  • Minimize looping — especially over shared data structures like message arrays, which are iterated frequently throughout the codebase. Every additional pass adds up at scale.
  • Consolidate sequential O(n) operations into a single pass whenever possible; never loop over the same collection twice if the work can be combined.
  • Choose data structures that reduce the need to iterate (e.g., Map/Set for lookups instead of Array.find/Array.includes).
  • Avoid unnecessary object creation; consider space-time tradeoffs.
  • Prevent memory leaks: careful with closures, dispose resources/event listeners, no circular references.

Backend Database Performance

  • On request startup and first page load paths, watch for serial database reads. Multiple round trips to MongoDB can add significant latency when the database is far from the app server.
  • Prefer passing already-loaded request/user/config data through helper functions instead of re-reading the same user, role, tenant, or principal data.
  • When two reads are independent, start them in parallel and gate the response on the authorization or validation result before returning data.
  • Keep authorization, permission, and tenant checks semantically identical when parallelizing reads. Speculative reads must remain scoped to the authenticated user or tenant and must not write to the response before validation succeeds.

Type Safety

  • Never use any. Explicit types for all parameters, return values, and variables.
  • Limit unknown — avoid unknown, Record<string, unknown>, and as unknown as T assertions. A Record<string, unknown> almost always signals a missing explicit type definition.
  • Don't duplicate types — before defining a new type, check whether it already exists in the project (especially packages/data-provider). Reuse and extend existing types rather than creating redundant definitions.
  • Use union types, generics, and interfaces appropriately.
  • All TypeScript and ESLint warnings/errors must be addressed — do not leave unresolved diagnostics.

Comments and Documentation

  • Write self-documenting code; no inline comments narrating what code does.
  • JSDoc only for complex/non-obvious logic or intellisense on public APIs.
  • Single-line JSDoc for brief docs, multi-line for complex cases.
  • Avoid standalone // comments unless absolutely necessary.

Import Order

Imports are organized into three sections:

  1. Package imports — sorted shortest to longest line length (react always first).
  2. import type imports — sorted longest to shortest (package types first, then local types; length resets between sub-groups).
  3. Local/project imports — sorted longest to shortest.

Multi-line imports count total character length across all lines. Consolidate value imports from the same module. Always use standalone import type { ... } — never inline type inside value imports.

JS/TS Loop Preferences

  • Limit looping as much as possible. Prefer single-pass transformations and avoid re-iterating the same data.
  • for (let i = 0; ...) for performance-critical or index-dependent operations.
  • for...of for simple array iteration.
  • for...in only for object property enumeration.

Frontend Rules (client/src/**/*)

Localization

  • All user-facing text must use useLocalize().
  • Only update English keys in client/src/locales/en/translation.json (other languages are automated externally).
  • Semantic key prefixes: com_ui_, com_assistants_, etc.

Components

  • TypeScript for all React components with proper type imports.
  • Semantic HTML with ARIA labels (role, aria-label) for accessibility.
  • Group related components in feature directories (e.g., SidePanel/Memories/).
  • Use index files for clean exports.

Theming and styling

  • Compose before styling. Search @librechat/client for an existing primitive, semantic variant, or composition before adding feature-local classes or CSS.
  • Use semantic roles. Colors and shared appearance values must come from the semantic Tailwind/theme roles. Do not add raw palette utilities, hard-coded hex/RGB/HSL colors, or light/dark-specific values in feature components.
  • Deepen the system when the need is reusable. Add a focused variant to a shared primitive or extend the canonical, versioned theme-token registry when multiple screens should share the same design decision. Do not create shallow local wrappers that merely relocate class strings.
  • Themes are data, not arbitrary CSS. Theme definitions may select semantic colors and shared appearance roles. They must not contain selectors, arbitrary CSS, application behavior, or alternate feature layouts. Preserve existing environment and stored-theme compatibility when changing the theme engine.
  • Keep layout and behavior local. Feature structure, responsive layout, state-driven transitions, and specialized visualization may remain feature-owned. Expose a theme role only when it represents a stable, reusable appearance decision; do not turn every measurement into a global token.
  • Treat custom CSS as an exception. Use it only when shared primitives and semantic utilities cannot express the requirement. Keep it narrowly scoped, consume theme variables where applicable, support light/dark and reduced motion, and add a brief code or PR explanation of why the exception is necessary.
  • Preserve defaults and prove variability. New theme-aware variants must reproduce the current default appearance unless a redesign is explicitly requested. Test semantic-token use and, when extending theme capabilities, include a deliberately different reference theme to prove that components adapt without feature-specific overrides.

Data Management

  • Feature hooks: client/src/data-provider/[Feature]/queries.ts → [Feature]/index.ts → client/src/data-provider/index.ts.
  • React Query (@tanstack/react-query) for all API interactions; proper query invalidation on mutations.
  • QueryKeys and MutationKeys in packages/data-provider/src/keys.ts.

Client State Ownership

The client is migrating from Recoil to Jotai. Convert the areas you touch rather than migrating wholesale, and split the work by who owns the state:

  • Feature-owned state — atoms a single feature both writes and reads. Convert these to Jotai as you touch them, and keep them inside the feature.
  • App-global state — preferences and shell state a feature merely consumes (maximizeChatSpace, showScrollButton, enterToSend, artifact visibility). A feature that could plausibly be extracted must not reach into ~/store for these; accept them through props or a small context the host supplies.

Passing app-global state in — rather than reaching for it — is what lets a feature move to its own workspace later without a rewrite, and it keeps the Jotai conversion scoped to the state a feature actually owns instead of dragging the global migration forward early.

Data-Provider Integration

  • Endpoints: packages/data-provider/src/api-endpoints.ts
  • Data service: packages/data-provider/src/data-service.ts
  • Types: packages/data-provider/src/types/queries.ts
  • Use encodeURIComponent for dynamic URL parameters.

Performance

  • Prioritize memory and speed efficiency at scale.
  • Cursor pagination for large datasets.
  • Proper dependency arrays to avoid unnecessary re-renders.
  • Leverage React Query caching and background refetching.

Backend Rules (api/**, packages/api/**)

Auth cache invalidation

When adding or changing code that mutates user documents, invalidate the auth user document cache for the affected users. This covers single-user updates as well as bulk role and user mutations. Without it, OpenID JWT request burst caching can serve a stale req.user until its TTL expires.

Development Commands

Command Purpose
npm run smart-reinstall Install deps (if lockfile changed) + build via Turborepo
npm run reinstall Clean install — wipe node_modules and reinstall from scratch
npm run backend Start the backend server
npm run backend:dev Start backend with file watching (development)
npm run build Build all compiled code via Turborepo (parallel, cached)
npm run frontend Build all compiled code sequentially (legacy fallback)
npm run frontend:dev Start frontend dev server with HMR (port 3090, requires backend running)
npm run build:data-provider Rebuild packages/data-provider after changes
  • Node.js: v24.16.0
  • Database: MongoDB
  • Backend runs on http://localhost:3080/; frontend dev server on http://localhost:3090/

Testing

  • Framework: Jest, run per-workspace.
  • Run tests from their workspace directory: cd api && npx jest <pattern>, cd packages/api && npx jest <pattern>, etc.
  • Frontend tests: __tests__ directories alongside components; use test/layout-test-utils for rendering.
  • Cover loading, success, and error states for UI/data flows.

Typechecking

  • A green build is not a typecheck. packages/api, packages/client and packages/data-schemas build with tsdown alone, which emits without checking types. Only packages/data-provider runs tsc as part of its build.
  • Run npx tsc --noEmit in the workspace you changed before calling it done. client also exposes it as npm run typecheck.
  • packages/client/tsconfig.json excludes *.spec.ts(x) and *.test.ts(x), so test files there are never typechecked — a type error in a spec surfaces only when the test runs.
  • npm run static-checks runs the Static Checks CI job locally against your staged files; npm run static-checks -- --against origin/dev reproduces what CI sees for a pull request, and npm run static-checks:full adds the slow gates (TypeScript, config migration tests, unused i18n keys, unused npm packages).

Philosophy

  • Real logic over mocks. Exercise actual code paths with real dependencies. Mocking is a last resort.
  • Spies over mocks. Assert that real functions are called with expected arguments and frequency without replacing underlying logic.
  • MongoDB: use mongodb-memory-server for a real in-memory MongoDB instance. Test actual queries and schema validation, not mocked DB calls.
  • MCP: use real @modelcontextprotocol/sdk exports for servers, transports, and tool definitions. Mirror real scenarios, don't stub SDK internals.
  • Only mock what you cannot control: external HTTP APIs, rate-limited services, non-deterministic system calls.
  • Heavy mocking is a code smell, not a testing strategy.

Formatting

Fix all formatting lint errors (trailing spaces, tabs, newlines, indentation) using auto-fix when available. All TypeScript/ESLint warnings and errors must be resolved.

npm run sort-imports with no arguments rewrites every file under api/, client/src and the four packages/*/src roots — far beyond what you touched. Always pass explicit paths: npm run sort-imports -- path/to/file.ts.