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Supabase's grants-based 42501 reaches existing projects after October 30, a post says
A dev.to author says Supabase's 42501 error from missing table grants will show up on existing projects after October 30, 2026. Adding an RLS policy does not clear that case, the author reports from local-stack tests, so telling it from the three policy causes means reading the message text.
The Engineer · Build desk
Card of HTTP statuses. An anon-key insert on a table with only a SELECT policy returned 401 with code 42501. A signed-in insert of someone else's id returned 403, with the same code and message as the 401. Across the policy cases, code 42501 also came back with 400.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Anon-key insert, only a SELECT policy, code 42501 | 401 HTTP status | 6 | |
| Signed-in insert of someone else's id | 403 HTTP status | same code and message as the 401 | 9 |
| Also seen with 42501 | 400 HTTP status | 13 |
What happened
- On a table with RLS on and no policies, a select returned 200 with an empty list and no error, so a missing read policy fails silently.
- With only an INSERT policy, insert() returned 201, but insert().select() returned 401 with 42501 and the whole insert rolled back.
- With no UPDATE policy, a second upsert on the same id returned 403, while a plain update() returned 200 and changed nothing.
Why it matters
- constraint Policy review is the usual response to 42501. The author says it does nothing for the grants case, so a team can finish that review and still have the error.
- exposure The post says existing projects are in scope. A project that has run clean for months is not exempt just because its policies have not changed.
- cost The same code arrives with 400, 401 or 403 in policy cases. Error handling that routes on HTTP status will misfile some of them.
- decision The October 30, 2026 date rests on one developer's post. Anyone scheduling work around it needs Supabase's own notice first.
42501 is Postgres's code for "insufficient privilege" [1]. Supabase returns it in two very different situations, and per the post the message text tells you which one you are in [2]. The HTTP status does not. Across the policy cases the author tested, the same code came back with 400, 401 and 403 [13]. A signed-out insert got 401, and a signed-in insert of someone else's id got 403 [9].
The policy causes are mechanical. RLS denies by default, per operation, so a table with only a SELECT policy can be read but not written [6]. Leave user_id out of an insert and the column is written as null. A check of auth.uid() = user_id then evaluates to something other than true, and the insert fails with 403 [10]. The author's fix there is a column default, set with alter table ... alter column user_id set default auth.uid() [10].
The grants case is different. The author says adding a policy does nothing for it, and says that was tested [15]. The post also says this case will show up on existing projects after October 30, 2026 [14]. That date is the only deadline in the material.
The post excerpt ends in its storage section, before the grants section. The reason for the date and the fix for the grants case are therefore not in the text. Supabase is not cited for the date, so it rests on one developer's post.
The tests ran on a local stack with supabase-js 2.117.2, CLI 2.120.0, Postgres 17.11 and PostgREST 16.4 [5]. The author says supabase-js called the real API for every row of the table [4]. The status codes transfer to a hosted project only if its PostgREST version returns the same ones. We'd check before routing on them.
In our view, a 42501 that survives policies for the right operations and roles points at grants. That follows from the author's finding that policies do nothing for that case [15]. The role condition matters because a policy written to authenticated does not apply to a request made with the anon key and no session [9].
What to watch
- A Supabase notice or docs page that confirms the October 30, 2026 date and says what changes for existing projects.
- The post's grants section: the exact error message for that case and the statement that fixes it.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence68
- Adoption
- Insufficient
- Hype gap−5
- Incentives
- Insufficient
- Confidence65
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
42501 is Postgres's code for "insufficient privilege".
- [2]
Supabase returns 42501 in two very different situations, and the error message tells you which one you are in.
- [3]
Of the situations the post lists, the first three are about policies and the last one is about grants.
- [4]
The author reproduced every row of the table on a local Supabase stack, with supabase-js calling the real API.
- [5]
Tests ran on supabase-js 2.117.2, Supabase CLI 2.120.0 (local stack), Postgres 17.11, PostgREST 16.4, Node 24.14.0 on Windows 11 Pro.
- [6]
Supabase's RLS denies by default, per operation: a table with RLS on and only a SELECT policy can be read but not written. An insert with the anon key returned 401 Unauthorized with code 42501 and a message naming the table.
- [7]
On a table with RLS and no policies at all, select() came back 200 with data: [] and no error.
- [8]
With only an INSERT policy on the table, insert() returned 201 Created, but insert().select() returned 401 with the same 42501 message; the whole insert was rolled back and left no rows behind.
- [9]
A policy written to the authenticated role does not apply to a request made with the anon key and no session. The profiles insert failed with 401 when signed out and with 403 when signed in but inserting someone else's id: same code, same message, different status.
- [10]
With a check of (select auth.uid()) = user_id, an insert that leaves user_id out writes null, and a signed-in insert failed with 403 and 42501. The cleaner fix is a column default: alter table public.todos alter column user_id set default auth.uid(), after which the same insert returned 201.
- [11]
With INSERT and SELECT policies but no UPDATE policy, the first upsert() returned 201 and the second on the same id returned 403 with a message mentioning the USING expression; a plain update() with no UPDATE policy returned 200, changed nothing, and gave back an empty list.
- [12]
Storage keeps files as rows in storage.objects, so uploads go through RLS; a bucket with no policy on that table refused an upload with a StorageApiError, status 400.
- [13]
Across the policy cases in the post, code 42501 came back with three distinct HTTP statuses: 400, 401 and 403.
- [14]
The grants case is the one that will suddenly show up on existing Supabase projects after October 30, 2026.
ReportedContestedSource: dev.to post by nils44344; single source2 sources— create a free account to open themView cited source - [15]
Adding a policy does nothing for the grants case, and the author says they tested that.
ReportedContestedSource: dev.to post by nils443442 sources— create a free account to open themView cited source
Sources
1 independent publisher whose own reporting we read for this story.
- dev.toSupabase error 42501: new row violates row-level security policy
1 article · October 13, 2026
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