computer-use-tool changedagents-and-tools/tool-use/computer-use-tool
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18281828### Manage screenshot history
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1830Long agent loops accumulate screenshots quickly (roughly 1,000–1,800 input tokens each). The API’s [request limits](https://platform.claude.com/docs/en/build-with-claude/vision#request-limits) also apply. Once a single request carries more than 20 images, every image in it is held to a stricter per-side limit. A loop that keeps its screenshot history reaches that count within a few dozen turns, so either resize each screenshot so that neither side exceeds 2000 px or prune older screenshots to keep 20 or fewer in the request.
1830Long agent loops accumulate screenshots quickly (roughly 1,000–1,800 input tokens each). The API’s [request limits](https://platform.claude.com/docs/en/build-with-claude/vision#request-limits) also apply. Once a single request carries more than 20 images, every image in it is held to a stricter per-side limit. A loop that keeps its screenshot history reaches that count within a few dozen turns, so either resize each screenshot to stay under that limit or prune older screenshots to keep 20 or fewer in the request.
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18321832To keep [Prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) effective while bounding context:
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18341834* Place one `cache_control` breakpoint after the system prompt and tool definitions, and up to three more on the last `tool_result` block of each of the most recent turns, advancing them each turn. Within a [batch action](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#batch-actions), markers on several blocks act as a single breakpoint, but each still counts toward the limit of four, so use at most one in any turn.
1835* Prune old screenshots in *batches*, not one each turn. Dropping a screenshot every turn changes the prefix every turn and invalidates the cache. A reasonable default is to keep the last three screenshots and prune every 25 turns, so the prefix stays byte-identical between prune events; if your screenshots exceed 2000 px on either side, choose an interval that keeps each request at 20 or fewer images.
1836* On Claude Fable 5.1, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5, avoid pruning on the client: removing an earlier screenshot [invalidates every later thinking block](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-in-conversation) in every request that still carries those turns. Resize screenshots to 2000 px or less per side instead, and use server-side [tool result clearing](https://platform.claude.com/docs/en/build-with-claude/context-editing#tool-result-clearing) to drop old ones from the context. If you must prune, keep [`prefix_mismatch_behavior: "drop_block"`](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-thinking-controls) set from then on; after each prune, Claude continues without the thinking produced since the pruned screenshot, on that request and every later one. On Claude Sonnet 5.5, `block_binding` works only with `thinking: {"type": "adaptive"}`. With `between_tools`, keep the history append-only, or strip the thinking blocks from the edited turn on. On Claude Haiku 5.5, `block_binding` works only with `thinking: {"type": "adaptive"}`; with `thinking: {"type": "disabled"}`, keep the history append-only, or strip the thinking blocks from the edited turn on.
1835* Prune old screenshots in *batches*, not one each turn. Dropping a screenshot every turn changes the prefix every turn and invalidates the cache. A reasonable default is to keep the last three screenshots and prune every 25 turns, so the prefix stays byte-identical between prune events; if your screenshots exceed the stricter limit, choose an interval that keeps each request at 20 or fewer images.
1836* On Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5, avoid pruning on the client: removing an earlier screenshot from a request [invalidates every later thinking block](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-in-conversation) in that request and in every later request. Resize screenshots to stay under the stricter limit instead and use server-side [tool result clearing](https://platform.claude.com/docs/en/build-with-claude/context-editing#tool-result-clearing) to drop old ones from the context. If you must prune, keep [`prefix_mismatch_behavior: "drop_block"`](https://platform.claude.com/docs/en/build-with-claude/thinking#preserved-thinking-controls) set from then on; after each prune, Claude continues without the thinking produced since the pruned screenshot, on that request and every later one. On Claude Sonnet 5.5 and Claude Haiku 5.5, `block_binding` works only with `thinking: {"type": "adaptive"}`. With any other thinking setting on those models, keep the history append-only or strip every `thinking` and `redacted_thinking` block after the pruned screenshot.
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18381838### Diagnose click issues
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