An API that returns 200 and does nothing is worse than one that returns an error

I cross-post my articles to dev.to. Looking at the numbers, the posts tagged agents were getting traffic and the one without it had a single view in twenty hours. Obvious fix: add agents to that post. I sent a PUT updating the tags. The response was 200. I opened the post. The tags were unchanged. Three requests, three 200s, three identical responses Assuming I'd malformed the request, I ran the smallest test I could: three PUTs to the same article, sending agents , then python,agents , then the original tags. All three returned 200. All three returned byte-identical bodies — the tags the post was created with. The truth: dev.to tags are immutable after publish, and the API silently ignores the field. Not a 403 saying you can't do that. Not a 422 saying the field is read-only. A 200, and then nothing happens. That one field made me wrong twice The first time was the day before. I'd sent 4 tags and gotten 3 back. My conclusion: dev.to caps tags at 3. That conclusion is entirely reasonable. You send four, you get three, what else would it be? I was confident enough to write MAX_TAGS = 3 into a script comment as an established fact. What actually happened: the tags field was never applied at all. What came back were the three tags from creation time. It had nothing to do with a cap. I could have sent one tag or ten and gotten the same three. One silently ignored field, two wrong conclusions in two days, and I committed one of them to source control as documentation for my future self. That's the real cost. Not the failed request — the false fact I wrote down as knowledge. Why 200 is more dangerous than an error An error interrupts you . It forces a stop, and it usually tells you something true. Even when the message is imprecise, "this did not work" is accurate information. A 200 doesn't interrupt you. You tick the step off and move on. You proceed on a false premise, believing you verified it. Going back through my ops log, this failure mode shows up more than once. A