Imported from jeremylongshore/tons-of-skills-marketplace (skills/.curated/supabase-common-errors/SKILL.md). Install upstream with npx skills add jeremylongshore/tons-of-skills-marketplace --skill supabase-common-errors. Copyright stays with the author (MIT).

Supabase Common Errors

Overview

Diagnostic guide for Supabase errors across PostgREST (PGRST*), PostgreSQL (numeric codes), Auth, Storage, and Realtime. Identify the error layer, trace the root cause, and apply the correct fix — every SDK call returns { data, error } where data is null when error exists.

The workflow is three steps: capture the error object, classify it by layer and code, then apply and verify the fix. Full step-by-step code lives in the diagnostic walkthrough; complete lookup tables are in the error reference.

Prerequisites

• @supabase/supabase-js installed (npm install @supabase/supabase-js)
• SUPABASE_URL and SUPABASE_ANON_KEY (or SUPABASE_SERVICE_ROLE_KEY) configured
• Access to Supabase Dashboard (for log inspection and SQL Editor)
• Supabase CLI installed for local development (npx supabase --version)

Instructions

Step 1 — Capture the Error Object

Every Supabase SDK call returns a { data, error } tuple. Never assume data exists — always destructure and check error first, because data is null whenever error is set.

const { data, error } = await supabase.from('todos').select('*')
if (error) {
  console.error(`[${error.code}] ${error.message}`)
  return  // data is null here — do not touch it
}
console.log(`Found ${data.length} rows`)

If error is undefined rather than null, upgrade to @supabase/supabase-js@2.x. See the walkthrough for the full guard pattern.

Step 2 — Identify the Error Layer and Code

Match the code prefix to its subsystem, then look it up in the Error Handling tables below:

• PGRST* → PostgREST (API gateway: JWT, query parsing, schema)
• 5-digit numeric (e.g. 42501, 23505) → PostgreSQL engine (RLS, constraints, migrations)
• AuthApiError → Auth service (credentials, confirmation, token expiry)
• StorageApiError → Storage service (bucket, RLS on storage.objects, size limits)

A missing code usually means the HTTP status is the signal: 401 → bad/missing SUPABASE_ANON_KEY; 500 → an unhandled exception in a database function. A paste-ready diagnoseSupabaseError() classifier is in the walkthrough.

Step 3 — Apply the Fix and Verify

Apply the fix from the matching Error Handling table, then re-run the original operation to confirm. Common recoveries:

• Refresh an expired JWT (PGRST301) with supabase.auth.refreshSession().
• Confirm an RLS block (42501) by re-querying with the service-role client before correcting the policy.
• After a migration, reload the PostgREST schema cache (Dashboard → Settings → API → "Reload schema cache", or NOTIFY pgrst, 'reload schema').

Full before/after fix code for both cases is in the walkthrough.

Output

Deliverables after applying this skill:

• Error identified by code and layer (PostgREST, PostgreSQL, Auth, Storage, Realtime)
• Root cause isolated using the diagnostic helper or manual code inspection
• Fix applied from the Error Handling table and verified against the original failing operation
• Guard code in place (if (error) checks) preventing silent null-data bugs

Error Handling

The two most-cited layers are inline below. Auth, Storage, and Realtime tables are in the full error reference.

PostgREST API Errors (PGRST*)

PostgreSQL Database Errors (5-digit codes)

Examples

The most common failure — calling .single() on optional data — is inline below. Three more worked examples (upsert to dodge 23505, Realtime subscription error handling, and serverless pool exhaustion) are in the examples reference.

Handling .single() on optional data (PGRST116)

// BAD — throws PGRST116 when the user has no profile row
const { data: profile } = await supabase
  .from('profiles').select('*').eq('user_id', userId).single()

// GOOD — returns null instead of erroring
const { data: profile, error } = await supabase
  .from('profiles').select('*').eq('user_id', userId).maybeSingle()

if (!profile) {
  await supabase.from('profiles').insert({ user_id: userId, display_name: 'New User' })
}

Resources

• Full diagnostic walkthrough — every capture/classify/fix code block
• Complete error reference — Auth, Storage, and Realtime tables
• Worked examples — upsert, Realtime, serverless pooling
• Supabase JavaScript SDK Reference
• PostgREST Error Codes
• PostgreSQL Error Codes
• RLS Debugging Guide
• Supabase Realtime Troubleshooting
• Supabase Status Page

Next Steps

• Use supabase-debug-bundle to generate a full diagnostic snapshot when errors persist after applying these fixes.
• Use supabase-security-basics to audit your RLS policies and prevent 42501 errors proactively.
• Use supabase-known-pitfalls for edge cases and SDK behavior that can cause subtle bugs.
• Use supabase-observability to set up logging and alerting so you catch errors before users report them.