Guides

HTTP status errors: handling 4xx and 5xx responses

A status error means the HTTP round trip worked — connection, TLS, request, response all succeeded — and the server used the status code to tell you something. Whether your client throws for it (axios rejects outside 2xx by default; fetch does not) is library policy, not protocol.

Whose bug is it?

Get the whole story

The status code is the headline; the response body and headers carry the actual diagnosis. Log them on failure — an error handler that logs only "Request failed with status code 400" discards the field-level detail the server already sent you. In axios that body is error.response.data; in fetch you must read it before throwing your own error.

Retry policy in one paragraph

Retry 429 (respecting Retry-After), 503, and 502/504 for idempotent requests, with exponential backoff and a cap. Never auto-retry 4xx — the request is wrong, and resending it is a louder way to be wrong. Treat an unexpected 4xx in production as a bug report about your own request construction, and an unexpected 5xx spike as the other side's incident: alert, degrade gracefully, and stop sending non-essential traffic while it lasts.

Documented occurrences

349 analyzed errors across 116 libraries match this failure class. Each links to the thrown message, its source line, and documented fixes.

SillyTavern/SillyTavern

• Gateway Timeout
• Internal server error
• Internal Server Error
• Internal Server Error
• Internal server error.
• +41 more in SillyTavern

jackwener/OpenCLI

• coingecko derivatives returned HTTP 429 (rate limited)
• coingecko returned HTTP 429 (rate limited)
• coingecko returned HTTP 429 (rate limited)
• coingecko returned HTTP 429 (rate limited)
• coingecko returned HTTP 429 (rate limited)
• +21 more in OpenCLI

Mintplex-Labs/anything-llm

• Internal Server Error
• Internal Server Error
• Internal Server Error
• Internal Server Error
• Internal Server Error
• +19 more in anything-llm

overleaf/overleaf

• Internal server error.
• Internal Server Error (addNotification failure res.sendStatus(500))
• Internal Server Error (cannot bulk remove by key res.sendStatus(500))
• Internal Server Error (cannot count by key res.sendStatus(500))
• Internal Server Error (compile and download pdf failed res.sendStatus(500))
• +18 more in overleaf

langfuse/langfuse

• Internal server error
• Internal server error
• Internal server error
• Internal server error
• Internal Server Error
• +13 more in langfuse

infiniflow/ragflow

• GitHub credential appears to be invalid or expired (HTTP 401).
• Insufficient permissions to access Bitbucket workspace (HTTP 403).
• Insufficient permissions to access Confluence resources (HTTP 403).
• Invalid or expired Bitbucket credentials (HTTP 401).
• Invalid or expired Confluence credentials (HTTP 401).
• +6 more in ragflow

BerriAI/litellm

• Internal Server Error.
• Internal server error: {e}
• Internal Server Error ({e})
• Internal Server Error({e})
• Internal Server Error, " + str(e)
• +2 more in litellm

hcengineering/platform

• err.message (fallback: 'Internal Server Error')
• err.message?.length > 0 ? err.message : 'Internal Server Error'
• Internal Server Error
• Internal server error
• Internal server error
• +2 more in platform

kubernetes/kubernetes

• internal server error
• Internal Server Error: %q: %v
• Internal Server Error: %#v
• internal server error: %v
• internal server error: %v
• +1 more in kubernetes

langgenius/dify

• Internal Server Error
• Internal Server Error
• Internal Server Error
• Internal Server Error
• Internal Server Error
• +1 more in dify

…and 106 more libraries — search for your exact message.

Other failure classes

• Connection failures: ECONNREFUSED, ECONNRESET, and friends
• DNS resolution errors: ENOTFOUND and getaddrinfo failures
• SSL/TLS and certificate errors
• Timeouts: ETIMEDOUT, deadlines, and hung requests
• Authentication and authorization failures
• Parsing and encoding errors: unexpected token, malformed input