The 302 Redirect Turned Your POST into a GET and Dropped the Body
Quick answer If your client sends a POST with a JSON body and the server responds with a 302, most HTTP clients follow the redirect automatically and reissue the request
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debugging
The 409 Conflict Was a Stale Version Field, Not a Duplicate Request
Quick answer: A 409 Conflict on an update is almost never "the server is broken." It is the server telling you that the resource changed between the moment
Read articleThe 504 Wasn't Our Code: Debugging an Upstream Gateway Timeout
Quick answer: A 504 Gateway Timeout means the edge proxy or load balancer gave up waiting for an upstream service, so the first thing to establish is which hop in
Read articleThe 404 Was a Base Path and a Trailing Slash the Client Quietly Dropped
Quick answer: A 404 that looks like a missing resource is often a routing problem in disguise: the client dropped a base path prefix, or a trailing slash changed which
Read articleThe URL Was Double-Encoded: Debugging a 400 from %2520
Quick answer: A 400 that only appears when a query value contains a space or a special character is usually double percent-encoding. The client encodes once, then a helper or
Read articleDebugging a 401: The Token Was Valid but the Audience Was Wrong
Quick answer: A 401 that arrives with a structurally perfect token almost always means the signature is fine but one of the token's claims does not match what
Read articleThe API Debugging Guide: Methods, Tools, and Common Failures
Quick answer: API debugging is the systematic work of locating where a request goes wrong — the client, the network, the gateway, or the service — by capturing the actual request and
Read articleThe agent appended a duplicate config key, and the last one silently won
The agent needed to raise the request timeout, so it appended a second timeout block to the config instead of editing the existing one. The lenient parser silently kept the last occurrence, and the first tuned value vanished without an error.
Read articleThe agent added validation after the write instead of before it
The agent added a guard to reject negative quantity, but placed it after the order was already saved. The standalone guard test went green while invalid rows kept landing in the table. A check that runs after the side effect protects nobody.
Read articleThe agent extracted a shared helper and merged two callers' error paths
Two routes shared an upstream call, so the agent lifted the block into one helper. The callers differed only on fault: one rethrew for a 500, the other served a cached fallback. The helper picked one exit, the harder caller silently degraded, and green tests missed it.
Read articleThe agent lowercased the lookup key and broke every case-sensitive record
The agent lowercased an opaque external id to fix inconsistent lookups, normalizing on write and read. New rows matched, existing mixed-case rows went missing and fell back to a default nobody noticed. Covers when normalization corrupts stored data and how to keep the canonical token intact.
Read articleThe agent wired the success path and left the failure branch silent
The agent implemented the happy path, returned 200, and declared done. The failure branch emitted nothing: no log, no trace, no surfaced error, so when it fired in production on-call had nothing to grep for. Covers a structured breadcrumb on every exit branch and verifying it under fault.
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