Reference

Errors

SQLSTATE codes and HTTP statuses, what causes each, and what to do.

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Where errors show

Client	Gets
Postgres (your app, psql)	an error with its SQLSTATE (`C`), message, and where it has them detail, hint, position, and the schema, table, column and constraint a violation names. A constraint error’s hint names the row: `Row bookings/7 already has this key.`
MCP (agents)	a normal result with `isError: true` and the message, which says how to fix the call
Platform API	an HTTP status and `{"error": "<code>", "message"}`: see Platform API
App auth	an HTTP status and `{"error", "message"}`: see Auth

Code	Means	Do
`40001`	rows changed on both sides since the fork; or both changed one table’s columns	read the dry run, then settle (`BY COLUMNS`, `RESOLVE`, `USING`) or redo the work on a fresh fork. See Conflicts
`23505`	both sides added rows with the same unique value	drop or change one side’s row
`23503`	the merged result has a row pointing at one the other side deleted	merge the deletion’s world after fixing the reference
`23514`	a `CHECK`, or a merge check found rows in the result (they’re in the message)	change the world until the check finds nothing
`55000`	the world isn’t at the `AT VERSION` given; a missing or wrong `CONFIRM DELETES`; a world open when the server stopped	read the diff again; give the count the message names; check `DIFF` then `CONFIRM`
`3D000`	no such world (also a Postgres connection to a database name that isn’t one)	`SHOW WORLDS`
`42710`	a world with that name exists	pick another name, or drop it
`2BP01`	dropping a world that has forks	merge or drop them, or `DROP WORLD … CASCADE`
`25001`	a world statement inside `BEGIN … COMMIT`	run it outside the transaction
`25006`	a write to a world as it was (`name@when`)	write to the world itself
`42601`	a world name with a dash, unquoted (`task-1`)	quote it: `"task-1"`
`42602`, `42939`	a world name that’s empty, has `@`, starts `_tx_`, or is a MERGE keyword	pick another name
`0A000`	merging or dropping `main`	`main` has no parent

Code	Means	Do
`42501`	an agent may not do this: it lacks the right (the message names it), the world isn’t its own, or it’s disabled	do it as a person, or change the agent’s rights
`42501`	`merging w needs a person’s review (merge policy p: …)`: its policy holds the merge; it’s queued	nothing is wrong: approve or discard it in Reviews
`42501`	a direct write to `main` by an agent keeping to a policy	write in a world and merge it
`42501`	outside the world’s declared scope	widen the scope (a person), or redo the work within it
`40001`	`… read rows that changed since it forked`: a stale read	redo the work in a new world forked from now

Code	Means	Do
`53400`	past the plan’s open worlds, or an agent writing too fast	drop worlds you’re done with; slow down
`53300`	too many connections or statements at once	use a pool; lower its size
`53200`	a query past its memory	narrow it, or add a `LIMIT`
`53100`	disk full: past the plan’s storage	delete data or worlds you don’t need
`57014`	`statement_timeout` passed, or canceled	index the filter, or raise the timeout for that session
`54001`	a regular expression that backtracks too long; recursion too deep	simplify the pattern; add a stop condition

Code	Means	Do
`22023`	a moment outside the history window (older than the plan keeps, or in the future)	pick a moment within it; restore a backup for older
`22P02`	`AS OF` given something that isn’t a time	`'-15 minutes'`, `'2026-10-20 09:00'`, a timestamp, or a parameter
`55000`	`RESTORE` to before the world’s last rebase	fork the past and merge what you need instead

Everything else is Postgres’s own code, with Postgres’s message:

Code	Means
`23502`, `23503`, `23505`, `23514`	not null, foreign key, unique, check
`42P01`, `42703`, `42883`, `42704`	no such table, column, function, object (the message lists what there is)
`42601`	syntax error, with its position
`42804`, `22P02`	a value of the wrong type, or text that isn’t one
`22003`, `22012`	out of range, division by zero
`25P02`	a statement after an error in the same transaction: roll back
`0A000`	a feature Chronos doesn’t have yet: see Known gaps
`28000`, `28P01`	TLS required (`sslmode=require`), or a wrong password

The message always ends with what happened to the data: nothing was merged.
It names up to 10 rows (orders/7, orders/9), and a dry run lists them all.
A held merge names every broken rule: it changes 40 rows (at most 3); it deletes 2 rows (at most 0).