Effect Deep Audit

Systematic methodology for bringing an Effect codebase to library-grade quality, battle-tested across full-stack audits covering auth, middleware, schemas, repos, event handlers, API groups, and tests.

Prerequisites (Optional)

• Effect source (recommended): git clone https://github.com/Effect-TS/effect for pattern verification
• Effect MCP: https://github.com/tim-smart/effect-mcp for API lookups (fallback: https://effect.website/docs)

The Process

Phase 1: Reconnaissance (DO THIS FIRST)

Verify against Effect source, not docs. Docs lag. Source is truth.

# Clone Effect source for pattern verification (if not already done)
# git clone https://github.com/Effect-TS/effect <effect-repo>

# Service patterns
rg "class .* extends Context\.Tag" <effect-repo>/packages/platform/src
rg "Effect\.Service" <effect-repo>/packages/cluster/src

# Error patterns
rg "Schema\.TaggedError" <effect-repo>/packages/cluster/src

# Layer composition
rg "Layer\.provideMerge" <effect-repo>/packages/platform/src

# HttpApi patterns
rg "HttpApiBuilder\.group" <effect-repo>/packages/platform/src
rg "HttpApiBuilder\.middleware" <effect-repo>/packages/platform/src

If you have effect-mcp configured, also use effect_docs_search({ query: "..." }) for API concepts.

Check what your framework already provides. Before writing custom code, grep the framework source. This is consistently the highest-leverage finding in audits — frameworks often provide operations that hundreds of lines of custom code reimplement.

# Example: check what capabilities your framework's plugins provide
rg "api\." <framework-source>/src/plugins/<plugin-name>/

Phase 2: Tiered Finding Classification

Audit every file in the target. Classify each finding:

Specific patterns to grep for:

# Tier 0: Bugs
rg "Effect\.log(Error|Warning|Info)\(" --type ts  # statement expressions (Effect not chained)
rg "as any" --type ts                              # type escapes hiding real errors

# Tier 2: Schema anti-patterns
rg "toModel|toXxx|toPublic" --type ts              # manual row mappers
rg "S\.Struct\({" --type ts                        # hand-written schemas (should be createSelectSchema)
rg "satisfies.*Schema" --type ts                   # schema-adjacent type assertions

# Tier 2: Error modeling
rg "Schema\.TaggedError" --type ts                 # check error patterns are correct

# Tier 3: Architecture
wc -l src/**/*.ts | sort -n | tail -10             # monolith files (>200 LOC)
rg "catchTag|catchTags|mapError" --type ts -c      # duplicated error handling

# Tier 4: Idioms
rg "DateTime\.unsafeNow" --type ts                 # should be DateTime.now (effectful)
rg "process\.env" --type ts                        # should use Config/Layer
rg "Effect\.sync.*unsafe" --type ts                # unnecessary sync wrapper
rg "withSpan" --type ts -c                         # span coverage (should be everywhere)

Phase 3: Plan as DAG

Structure the plan as a dependency graph. Key insight: type errors cascade. Changing a schema breaks every consumer. Changing a service interface breaks every implementation. Work bottom-up:

Layer 0: Foundation (schemas, table defs, branded types)
Layer 1: Service interfaces + middleware
Layer 2: Implementations (repos, event handlers)
Layer 3: API handlers (group files)
Layer 4: Tests
Layer 5: Cleanup (spans, idioms, dead code)

Each layer gates on: 0 type errors + all tests passing. Do NOT proceed to the next layer with errors. The type checker is your friend — it tells you every callsite that needs updating.

Phase 4: Execution

Parallelize mechanical work. Schema renames, import fixes, field renames across 20 files — these are perfect for parallel agents. Save judgment-heavy work for files that require it (handler rewrites, middleware logic, layer composition).

Keep tests green. Run tsc --noEmit + vitest run after EVERY structural change. If you have 14 errors, fix all 14 before moving on. Compounding errors across layers is how 3-hour debugging sessions happen.

Delete aggressively. No backwards compat shims. No renamed _unused vars. No // removed comments. If code is dead, rm it. Git has history.

Key Patterns Discovered

createSelectSchema = sole schema source of truth

Every API response schema derives from a Drizzle table:

import { createSelectSchema } from 'drizzle-orm/effect-schema'

const OwnedAssetSelect = createSelectSchema(ownedAssets, {
  id: OwnedAssetId,           // branded type override
  ownerUserId: UserId,        // branded type override
  kind: OwnedAssetKind,       // literal union override
  createdAt: Schema.DateTimeUtc,  // NOT DateTimeUtcFromDate (breaks HTTP JSON)
}).omit('metadata', 'sourceEventId')

Critical: Use Schema.DateTimeUtc (Encoded=string), NOT Schema.DateTimeUtcFromDate (Encoded=Date). DateTimeUtcFromDate breaks HTTP JSON round-trips because the encoded form is a Date object, not a string. This bug was found in multiple domain packages during audits.

Nullable columns with overrides need S.NullOr() wrapping — the override replaces the full column schema including auto-nullability.

Handlers decode inline — no mapper functions:

return yield* S.decodeUnknown(MySchema)(row).pipe(Effect.orDie)

Single middleware pattern

One middleware that: resolves session, checks authorization, provides context. Not two middlewares where the second re-resolves what the first already resolved.

Effect.logError is an Effect, not a statement

// BUG: creates Effect value, discards it
Effect.logError('something broke', { error })
return Effect.succeed(fallbackResponse)

// FIX: chain it
Effect.logError('something broke', { error }).pipe(
  Effect.as(fallbackResponse)
)

Tracing

• Use Effect.fn("Service.method") for service method definitions (preferred — combines function definition + automatic span)
• Use Effect.withSpan only when wrapping existing effects in pipe chains
• Add Effect.annotateLogs("service", "ServiceName") to every service module

// Preferred: Effect.fn for service methods
findById: Effect.fn("UserRepository.findById")(function*(userId) {
  const rows = yield* sql`SELECT * FROM users WHERE id = ${userId}`
  if (rows.length === 0) return yield* new UserNotFound({ userId })
  return yield* Schema.decodeUnknown(User)(rows[0])
}),

// Fallback: withSpan for pipe chains
listByOwner: (userId, limit = 100) =>
  db.select().from(table).where(...).pipe(
    Effect.mapError(toRepositoryQueryError(REPO, 'listByOwner')),
    Effect.flatMap(Effect.forEach((row) => decode(row).pipe(Effect.orDie))),
    Effect.withSpan('OwnedAssetRepository.listByOwner'),
  ),

Monolith handler files -> one file per API group

A 500-line handler file with all routes is unnavigable. Split into:

• groups/HealthGroupLive.ts
• groups/AdminGroupLive.ts
• groups/UserManagementGroupLive.ts
• etc.

The main handler file becomes pure layer wiring (~30-50 lines).

Shared error helpers go in a dedicated module, not duplicated across group files.

DateTime.now vs DateTime.unsafeNow

DateTime.unsafeNow() is sync. DateTime.now is effectful. In Effect.gen contexts, always use yield* DateTime.now. The "unsafe" prefix exists for a reason — it bypasses the Effect runtime's clock, which matters for testing and time-travel debugging.

Checklist (run after every audit)

[ ] Every API response schema uses createSelectSchema, not manual S.Struct
[ ] Every DateTimeUtc column uses S.DateTimeUtc (not DateTimeUtcFromDate)
[ ] Every nullable column with a branded override uses S.NullOr()
[ ] No toXxx mapper functions — handlers decode inline with S.decodeUnknown
[ ] No as any / as unknown type escapes in non-test code
[ ] No Effect.logError/logWarning as statement expressions
[ ] No process.env — all config through Effect Config/Layer
[ ] No DateTime.unsafeNow in Effect.gen contexts
[ ] Every service method uses Effect.fn (or Effect.withSpan for pipe chains)
[ ] Every service module has Effect.annotateLogs
[ ] No handler files > 200 LOC — split into per-group files
[ ] No duplicated error mapping helpers — extract to shared module
[ ] Tests split into per-group files with shared test infrastructure
[ ] Framework capabilities audited before writing custom code
[ ] Dead code deleted (not commented out, not renamed with _prefix)

References