Errors & fixes

The errors developers actually hit while building against Claude, catalogued with what causes each one and the one-line fix — not a restatement of the API reference's parameter list. Each entry names the exact error shape you'd see in a response or a stack trace, so it's the kind of page worth bookmarking or linking from a Slack thread the moment you hit it, rather than one you'd read end to end.

Nearly every entry here traces back to one of two root causes: a parameter or behaviour that existed on an older model generation and was removed or changed on a newer one, or a limit — a token count, a breakpoint count, a lookback window — that a request quietly exceeded with no error at all, which is arguably worse than an error because nothing tells you it happened. The catalogue grows mostly from what readers report actually hitting in production, via contact, so if you hit something specific that isn't listed here yet, that report is the fastest way it gets added.

Where an entry involves a model-generation change specifically, it links to the fuller migration guide in /prompting/ — the error page is the fast fix; the migration guide is the full picture if you're moving a whole codebase rather than patching one call site.