Atlas webfetch fails with Response too large (exceeds 5MB limit) because webfetch checks content-length first and then the actual arrayBuffer byteLength against MAX_RESPONSE_SIZE, so a server that lies about or omits content-length is still caught after download. The fix is to fetch a narrower URL, an API endpoint or a specific page rather than a whole dump, and to request format: "text" or "markdown" so the Accept header steers the server toward a smaller representation.
Why does Atlas report Response too large (exceeds 5MB limit)
Atlas reports Response too large (exceeds 5MB limit) because webfetch checks content-length first and then the actual arrayBuffer byteLength against MAX_RESPONSE_SIZE. Both checks exist in the 2026 source, so a server that lies about or omits content-length is still caught after download.
There are two distinct rejection points inside Atlas webfetch, and knowing which one fired tells you what to change. The first is the content-length header: when the server advertises a body past MAX_RESPONSE_SIZE, webfetch refuses before reading the body, and the error is instant. The second is the measured arrayBuffer byteLength after the response has been read, which catches servers that omit content-length entirely or understate it. If your failure took a while to arrive, the second check fired, which means the bytes really were on the wire. Either way the resource is simply bigger than the limit, and the resolution is to ask for less.
How to fix Response too large in Atlas webfetch
Fix Response too large (exceeds 5MB limit) in Atlas by fetching a narrower URL: an API endpoint or a specific page rather than a whole dump. Then request format: "text" or "markdown" so the Accept header steers the server toward a smaller representation of the same resource.
Narrowing the URL is the highest-leverage change. A documentation index, a full sitemap, or an export endpoint frequently ships megabytes of markup that you did not need. Point Atlas webfetch at the single page or the JSON API route that answers your question instead. The format parameter is the second lever: requesting format: "text" or format: "markdown" sets an Accept header that many servers honor by returning a leaner representation, which can bring a response under MAX_RESPONSE_SIZE without changing the URL. Be honest about the caveat: format is a request, not a guarantee. A server that ignores Accept will still send the same oversized body, and webfetch will still reject it on the arrayBuffer byteLength check.
How to download a large file with bash instead of Atlas webfetch
For very large assets, download with bash and process the file locally instead of routing bytes through Atlas webfetch. The MAX_RESPONSE_SIZE ceiling that produces Response too large (exceeds 5MB limit) applies to webfetch, so a file that legitimately exceeds it belongs on disk, not in a tool response.
Multi-megabyte archives, database dumps, model weights, and CSV exports are not content an agent should be reading in one gulp anyway. Fetch them with bash, write them to disk, and then have Atlas work against the file with read, grep, and glob. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, so the bash download is subject to the same approvals as any other command. Once the asset is local, you can slice out only the region you care about instead of paying the size ceiling on every retry.
How to verify the Atlas webfetch size fix worked
Verify the Atlas webfetch fix by re-running the call: a successful fetch returns content instead of Response too large (exceeds 5MB limit). If the error still appears after narrowing the URL, the resource is still over MAX_RESPONSE_SIZE and the next step is pagination or a bash download.
Confirmation is binary here. Either webfetch returns the body, in which case both the content-length check and the arrayBuffer byteLength check passed, or it repeats the same message. Watch the timing on a repeat failure: an instant rejection means the server advertised an oversized content-length, while a delayed one means the download completed and the measured byteLength was still too big. A delayed failure after you added format: "text" is a strong hint that the server ignored the Accept header, and that the URL itself, not the representation, is what has to change.
How to use a paginated endpoint with Atlas webfetch
Retry against a paginated endpoint if the site offers one: each Atlas webfetch call then pulls a single page that stays under MAX_RESPONSE_SIZE, instead of one request that trips Response too large (exceeds 5MB limit). Pagination is the cleanest fix when the data really is needed in full.
Many APIs expose page or cursor parameters precisely because clients cannot hold an entire collection in memory. Walk the pages with successive Atlas webfetch calls and let the agent accumulate what it needs. Pagination also plays well with how Atlas works, because Atlas fans out work to subagents that can run in the foreground or in parallel background sessions, so a long crawl does not have to block the main conversation. If the site offers no pagination and no narrower route, fall back to downloading with bash and processing the file locally.
How to fix it
- 01Fetch a narrower URL: an API endpoint or a specific page rather than a whole dump.
- 02Request format: "text" or "markdown" so the Accept header steers the server toward a smaller representation.
- 03For very large assets, download with bash and process the file locally instead of pulling the bytes through webfetch.
- 04Retry against a paginated endpoint if the site offers one, so each webfetch call stays under MAX_RESPONSE_SIZE.
Frequently asked questions
- how to fix Response too large (exceeds 5MB limit) in Atlas
- Fetch a narrower URL, an API endpoint or a specific page rather than a whole dump, and request format: "text" or "markdown" so the Accept header steers the server toward a smaller representation.
- can I raise the Atlas webfetch MAX_RESPONSE_SIZE limit
- Atlas webfetch enforces MAX_RESPONSE_SIZE against both content-length and the measured arrayBuffer byteLength. Rather than fighting the ceiling, fetch a narrower URL, use a paginated endpoint, or download the asset with bash and process it locally.
- why does Atlas webfetch fail only after the download finishes
- Atlas webfetch checks content-length first and then the actual arrayBuffer byteLength against MAX_RESPONSE_SIZE. A server that omits or understates content-length passes the first check and is caught by the second, after the body has been read.
- does the format parameter make Atlas webfetch responses smaller
- Requesting format: "text" or "markdown" sets an Accept header that steers the server toward a smaller representation. It helps when the server honors Accept, but a server that ignores it will still return an oversized body.
- how do I fetch a large file for Atlas to analyze
- Download it with bash and process the file locally. The webfetch size ceiling applies to tool responses, so large assets belong on disk where Atlas can read and grep them.
- does pagination help with the Atlas webfetch size error
- Yes. Retry against a paginated endpoint if the site offers one, so each webfetch call returns a single page that stays under the size limit instead of one oversized response.
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