NoOutputGeneratedError [AI_NoOutputGeneratedError]: No output generated.
This does not mean the model returned nothing. In both of the reports this page is built from, the model had just returned a tool call — and the structured-output parser only ran on a step that ended in text. The run stopped one step short of the thing you asked for. Every claim below is quoted from one of three pages on the AI SDK’s own repository, each fetched on 7 October 2026, each with its address given.
The first of the two reports is vercel/ai issue #10235, opened 14 November 2025. The reporter was calling generateText with tools from a remote MCP server and output: Output.object({ schema }), and wrote, verbatim:
If I pass tools to generateText, I’m getting NoOutputGeneratedError [AI_NoOutputGeneratedError]: No output generated. error. If I don’t pass any tools it seems to work, as in I’m getting some output.
That second sentence is the whole diagnosis, and it was arrived at by the cheapest possible experiment: remove the tools, run the same prompt, watch the error go away. The same report then names the branch responsible:
Looks like generateText parses the output only when the last step is “stop”. In my case it’s “tool-calls”.
And it records what happens if you simply widen that branch, which is worth knowing before you try it yourself: “Updating the relevant if statement in the ai library to parse the output in this case doesn’t solve the problem, as lastStep.text is empty, so the parsing (outputSpecification.parseCompleteOutput) fails.” A tool-call step has no text to parse. The reported version was ai: 6.0.0-beta.98.
Issue #13075, opened 4 March 2026, hits it through a step budget rather than through MCP. The reporter was running a tool loop with stopWhen: stepCountIs(6), two tools, and a configured object output, and describes it like this:
LoopAgent called tools several times, ultimately reaching the limit of 6 steps and returning the last tool_result which triggered AI_NoOutputGeneratedError immediatly
The trace pasted into that report carries the one field that identifies this failure from the outside: 'ai.response.finishReason': 'tool-calls'. Two different routes in — a tool-heavy prompt in one, a step cap in the other, 110 days apart — and the same last step. That is the signature. If the run ended on a tool call and you asked for structured output, you get this string.
The proposed fix is pull request #21774, opened 29 September 2026 by the repository’s own automation and marked a contributor change. Its description states the cause in two sentences:
ToolLoopAgent and generateText could stop on a tool-call step and throw AI_NoOutputGeneratedError despite a configured structured output. The loop exited as soon as stopWhen matched, while output parsing rejected the final tool-calls step.
Read that as a race between two rules that were never introduced to each other. One rule says stop now, the moment the stop condition matches. The other says parse the output, but only off a step that ended in text. When the step that matched the stop condition was a tool call, the first rule fires and the second refuses, and the thing you get is an exception rather than either the output or the tool result.
This matters for what you do next, so here is the measurement rather than an impression. On the pages fetched on 7 October 2026: the state field on pull request #21774 reads OPEN, and issue #13075 is listed as Open where the pull request references it. The pull request was opened 209 days after the second report and 319 days after the first.
So do not plan on an upgrade being the fix today. Check the state of that pull request yourself before you decide — it is one page and it is the authoritative copy, whereas this one is a reading of it taken on a single day. What the pull request does tell you, regardless of whether it has landed by the time you read this, is which shape the people who own the code consider correct. That is useful even as a patch you write yourself.
The pull request’s own summary describes the remedy:
Added a final tool-disabled model call with toolChoice none when an explicit output is configured and a stop condition is reached, then parse that response as the requested output.
Do that in your own code and you do not need to wait for anything. When your loop ends, look at the last step. If it ended in a tool call and you want structured output, make one more model call with the tools switched off, hand it the conversation including the final tool result, and parse that for your object. One extra call, and the parser now gets a step that ended in text, which is the only kind it accepts.
Or stop asking for structured output at the end of a tool loop. If the last tool already returned the data you need, read it off the tool result and skip the parse entirely. This is usually the cheaper answer and it removes the failure mode instead of handling it.
Do not simply raise the step cap. Issue #13075’s run stopped the instant stepCountIs(6) matched; a cap of twelve just moves the same cliff six steps to the right, and a loop that wanted to call another tool will still be mid-tool-call when it arrives. The cap is not what is wrong. What is wrong is that the run is allowed to end on a tool call.
None of these needs a claim about the library’s internals, which is deliberate: a procedure that only reads your own run cannot be wrong about someone else’s release.
The thing worth keeping even if you never see this string again: a tool loop has two different ways to be finished, and they are not the same event. “The budget is used up” is not “the answer is ready”. Any loop that can be cut off by a counter needs an explicit final step whose job is to turn whatever state it is in into the answer — otherwise the cut-off and the answer are competing for the same moment, which is the race this error reports.
If your run did not throw but handed you a finish reason you did not expect, the string to look up is the reason itself: finishReason: 'tool-calls' is the same step seen from the other side, where nothing was thrown at all. If it ended because the model ran out of room rather than out of steps, that is finishReason: 'length', 'content-filter', 'error', 'other'.
There is a written guide: the step-and-turn arithmetic as a formula you can run against a brief before you launch it, why raising a cap does not finish the job — the exact mistake this page argues against — and batch.py, one standard-library file that collapses a per-item loop into a single pass, which also removes the problem on this page, because a single pass has no final tool-call step to be cut off on. It is $19, on a storefront that delivers the files automatically and carries a 30-day money-back guarantee (checked 2 October 2026). One working way to pay today is 19 USDC on Base, and delivery is manual: you email the transaction hash and the files come back as a reply. This page is free, ungated, and sells nothing on its own.
The short version: AI_NoOutputGeneratedError fires when a run with a configured structured output ends on a tool-call step, because the parser only reads a step that ended in text. Two reports on the SDK’s repository say so — #10235 of 14 November 2025 (“parses the output only when the last step is ‘stop’… in my case it’s ‘tool-calls’”) and #13075 of 4 March 2026 — and the vendor’s own pull request #21774 says the loop “exited as soon as stopWhen matched, while output parsing rejected the final tool-calls step”. On the copies we read on 7 October 2026 that pull request is still open. The fix you can apply today is the one it proposes: after the loop stops, make one more model call with tools disabled and parse that for your output.
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