When you need to show edits as a real diff, prefer the diffs tool instead of writing a manual summary.
The diffs tool accepts either before + after text, or a unified patch string.
Use mode=view when you want an interactive gateway-hosted viewer. After the tool returns, use details.viewerUrl with the canvas tool via canvas present or canvas navigate.
If the deployment uses a loopback trusted proxy (for example Tailscale Serve with gateway.trustedProxies including 127.0.0.1), raw loopback viewer requests can fail closed without forwarded client-IP headers. In that topology, prefer mode=file / mode=both, or use a configured viewerBaseUrl / explicit proxy/public baseUrl when you need a shareable viewer URL.
Use mode=file when you need a rendered file artifact. Set fileFormat=png (default) or fileFormat=pdf. The tool result includes details.filePath.
For large or high-fidelity files, use fileQuality (standard|hq|print) and optionally override fileScale/fileMaxWidth.
When you need to deliver the rendered file to a user or channel, do not rely on the raw tool-result renderer. Instead, call the message tool and pass details.filePath through path or filePath.
Use mode=both when you want both the gateway viewer URL and the rendered artifact.
If the user has configured diffs plugin defaults, prefer omitting mode, theme, layout, and related presentation options unless you need to override them for this specific diff.
Include path for before/after text when you know the file name.