feat: add provider-specific file reading limits (maxReadFileLine)

Add a per-provider maxReadFileLine setting that allows users to override
the default 2000-line limit when reading files. This helps users with
slower local providers (e.g. CPU-based inference) avoid timeouts by
reducing prompt size.

Changes:
- Add maxReadFileLine to baseProviderSettingsSchema (packages/types)
- Update createReadFileTool() to reflect the effective limit in tool description
- Thread the setting through getNativeTools() and buildNativeToolsArray()
- Enforce the limit at execution time in ReadFileTool.processTextFile()
- Apply the limit to @ mention file reads via parseMentions chain
- Add MaxReadFileLineControl UI component in provider advanced settings
- Add English localization keys for the new setting
- Fix affected tests to account for new parameter

Closes #11407

packages/types/src/provider-settings.ts

@@ -189,6 +189,9 @@ const baseProviderSettingsSchema = z.object({
 
 	// Model verbosity.
 	verbosity: verbosityLevelsSchema.optional(),
+
+	// File reading limits.
+	maxReadFileLine: z.number().int().min(1).optional(),
 })
 
 // Several of the providers share common model config properties.

src/core/mentions/__tests__/processUserContentMentions.spec.ts

@@ -223,6 +223,7 @@ describe("processUserContentMentions", () => {
 				false, // showRooIgnoredFiles should default to false
 				true, // includeDiagnosticMessages
 				50, // maxDiagnosticMessages
+				undefined, // maxReadFileLine
 			)
 		})
 
@@ -251,6 +252,7 @@ describe("processUserContentMentions", () => {
 				false,
 				true, // includeDiagnosticMessages
 				50, // maxDiagnosticMessages
+				undefined, // maxReadFileLine
 			)
 		})
 	})

src/core/mentions/index.ts

@@ -105,7 +105,8 @@ export interface ParseMentionsResult {
  * Formats file content to look like a read_file tool result.
  * Includes Gemini-style truncation warning when content is truncated.
  */
-function formatFileReadResult(filePath: string, result: ExtractTextResult): string {
+function formatFileReadResult(filePath: string, result: ExtractTextResult, maxReadFileLine?: number): string {
+	const effectiveLimit = maxReadFileLine ?? DEFAULT_LINE_LIMIT
 	const header = `[read_file for '${filePath}']`
 
 	if (result.wasTruncated && result.linesShown) {
@@ -114,7 +115,7 @@ function formatFileReadResult(filePath: string, result: ExtractTextResult): stri
 		return `${header}
 IMPORTANT: File content truncated.
 Status: Showing lines ${start}-${end} of ${result.totalLines} total lines.
-To read more: Use the read_file tool with offset=${nextOffset} and limit=${DEFAULT_LINE_LIMIT}.
+To read more: Use the read_file tool with offset=${nextOffset} and limit=${effectiveLimit}.
 
 File: ${filePath}
 ${result.content}`
@@ -134,6 +135,7 @@ export async function parseMentions(
 	showRooIgnoredFiles: boolean = false,
 	includeDiagnosticMessages: boolean = true,
 	maxDiagnosticMessages: number = 50,
+	maxReadFileLine?: number,
 ): Promise<ParseMentionsResult> {
 	const mentions: Set<string> = new Set()
 	const validCommands: Map<string, Command> = new Map()
@@ -249,6 +251,7 @@ export async function parseMentions(
 					rooIgnoreController,
 					showRooIgnoredFiles,
 					fileContextTracker,
+					maxReadFileLine,
 				)
 				contentBlocks.push(fileResult)
 			} catch (error) {
@@ -331,6 +334,7 @@ async function getFileOrFolderContentWithMetadata(
 	rooIgnoreController?: any,
 	showRooIgnoredFiles: boolean = false,
 	fileContextTracker?: FileContextTracker,
+	maxReadFileLine?: number,
 ): Promise<MentionContentBlock> {
 	const unescapedPath = unescapeSpaces(mentionPath)
 	const absPath = path.resolve(cwd, unescapedPath)
@@ -358,7 +362,8 @@ async function getFileOrFolderContentWithMetadata(
 				}
 			}
 			try {
-				const result = await extractTextFromFileWithMetadata(absPath)
+				const effectiveLimit = maxReadFileLine ?? DEFAULT_LINE_LIMIT
+				const result = await extractTextFromFileWithMetadata(absPath, effectiveLimit)
 
 				// Track file context
 				if (fileContextTracker) {
@@ -368,7 +373,7 @@ async function getFileOrFolderContentWithMetadata(
 				return {
 					type: "file",
 					path: mentionPath,
-					content: formatFileReadResult(mentionPath, result),
+					content: formatFileReadResult(mentionPath, result, maxReadFileLine),
 					metadata: {
 						totalLines: result.totalLines,
 						returnedLines: result.returnedLines,
@@ -415,8 +420,12 @@ async function getFileOrFolderContentWithMetadata(
 						try {
 							const isBinary = await isBinaryFile(absoluteFilePath).catch(() => false)
 							if (!isBinary) {
-								const result = await extractTextFromFileWithMetadata(absoluteFilePath)
-								fileReadResults.push(formatFileReadResult(filePath.toPosix(), result))
+								const effectiveFolderLimit = maxReadFileLine ?? DEFAULT_LINE_LIMIT
+								const result = await extractTextFromFileWithMetadata(
+									absoluteFilePath,
+									effectiveFolderLimit,
+								)
+								fileReadResults.push(formatFileReadResult(filePath.toPosix(), result, maxReadFileLine))
 							}
 						} catch (error) {
 							// Skip files that can't be read

src/core/mentions/processUserContentMentions.ts

@@ -36,6 +36,7 @@ export async function processUserContentMentions({
 	showRooIgnoredFiles = false,
 	includeDiagnosticMessages = true,
 	maxDiagnosticMessages = 50,
+	maxReadFileLine,
 }: {
 	userContent: Anthropic.Messages.ContentBlockParam[]
 	cwd: string
@@ -45,6 +46,7 @@ export async function processUserContentMentions({
 	showRooIgnoredFiles?: boolean
 	includeDiagnosticMessages?: boolean
 	maxDiagnosticMessages?: number
+	maxReadFileLine?: number
 }): Promise<ProcessUserContentMentionsResult> {
 	// Track the first mode found from slash commands
 	let commandMode: string | undefined
@@ -72,6 +74,7 @@ export async function processUserContentMentions({
 							showRooIgnoredFiles,
 							includeDiagnosticMessages,
 							maxDiagnosticMessages,
+							maxReadFileLine,
 						)
 						// Capture the first mode found
 						if (!commandMode && result.mode) {
@@ -116,6 +119,7 @@ export async function processUserContentMentions({
 								showRooIgnoredFiles,
 								includeDiagnosticMessages,
 								maxDiagnosticMessages,
+								maxReadFileLine,
 							)
 							// Capture the first mode found
 							if (!commandMode && result.mode) {
@@ -166,6 +170,7 @@ export async function processUserContentMentions({
 											showRooIgnoredFiles,
 											includeDiagnosticMessages,
 											maxDiagnosticMessages,
+											maxReadFileLine,
 										)
 										// Capture the first mode found
 										if (!commandMode && result.mode) {

src/core/prompts/tools/native-tools/index.ts

@@ -32,6 +32,8 @@ export type { ReadFileToolOptions } from "./read_file"
 export interface NativeToolsOptions {
 	/** Whether the model supports image processing (default: false) */
 	supportsImages?: boolean
+	/** Provider-specific override for the maximum lines returned per read */
+	maxReadFileLine?: number
 }
 
 /**
@@ -41,10 +43,11 @@ export interface NativeToolsOptions {
  * @returns Array of native tool definitions
  */
 export function getNativeTools(options: NativeToolsOptions = {}): OpenAI.Chat.ChatCompletionTool[] {
-	const { supportsImages = false } = options
+	const { supportsImages = false, maxReadFileLine } = options
 
 	const readFileOptions: ReadFileToolOptions = {
 		supportsImages,
+		maxReadFileLine,
 	}
 
 	return [

src/core/prompts/tools/native-tools/read_file.ts

@@ -34,6 +34,8 @@ function getReadFileSupportsNote(supportsImages: boolean): string {
 export interface ReadFileToolOptions {
 	/** Whether the model supports image processing (default: false) */
 	supportsImages?: boolean
+	/** Provider-specific override for the maximum lines returned per read (default: DEFAULT_LINE_LIMIT) */
+	maxReadFileLine?: number
 }
 
 // ─── Schema Builder ───────────────────────────────────────────────────────────
@@ -58,7 +60,10 @@ export interface ReadFileToolOptions {
  * @returns Native tool definition for read_file
  */
 export function createReadFileTool(options: ReadFileToolOptions = {}): OpenAI.Chat.ChatCompletionTool {
-	const { supportsImages = false } = options
+	const { supportsImages = false, maxReadFileLine } = options
+
+	// Compute the effective line limit for the tool description
+	const effectiveLineLimit = maxReadFileLine ?? DEFAULT_LINE_LIMIT
 
 	// Build description based on capabilities
 	const descriptionIntro =
@@ -70,7 +75,7 @@ export function createReadFileTool(options: ReadFileToolOptions = {}): OpenAI.Ch
 		` PREFER indentation mode when you have a specific line number from search results, error messages, or definition lookups - it guarantees complete, syntactically valid code blocks without mid-function truncation.` +
 		` IMPORTANT: Indentation mode requires anchor_line to be useful. Without it, only header content (imports) is returned.`
 
-	const limitNote = ` By default, returns up to ${DEFAULT_LINE_LIMIT} lines per file. Lines longer than ${MAX_LINE_LENGTH} characters are truncated.`
+	const limitNote = ` By default, returns up to ${effectiveLineLimit} lines per file. Lines longer than ${MAX_LINE_LENGTH} characters are truncated.`
 
 	const description =
 		descriptionIntro +
@@ -125,7 +130,7 @@ export function createReadFileTool(options: ReadFileToolOptions = {}): OpenAI.Ch
 		},
 		limit: {
 			type: "integer",
-			description: `Maximum number of lines to return (slice mode, default: ${DEFAULT_LINE_LIMIT})`,
+			description: `Maximum number of lines to return (slice mode, default: ${effectiveLineLimit})`,
 		},
 		indentation: {
 			type: "object",

src/core/task/Task.ts

@@ -2800,6 +2800,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				showRooIgnoredFiles,
 				includeDiagnosticMessages,
 				maxDiagnosticMessages,
+				maxReadFileLine: this.apiConfiguration?.maxReadFileLine,
 			})
 
 			// Switch mode if specified in a slash command's frontmatter

src/core/task/build-tools.ts

@@ -114,6 +114,7 @@ export async function buildNativeToolsArrayWithRestrictions(options: BuildToolsO
 	// Build native tools with dynamic read_file tool based on settings.
 	const nativeTools = getNativeTools({
 		supportsImages,
+		maxReadFileLine: apiConfiguration?.maxReadFileLine,
 	})
 
 	// Filter native tools based on mode restrictions.

src/core/tools/ReadFileTool.ts

@@ -216,7 +216,8 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 					// (they become U+FFFD replacement characters instead of throwing)
 					const buffer = await fs.readFile(fullPath)
 					const fileContent = buffer.toString("utf-8")
-					const result = this.processTextFile(fileContent, entry)
+					const providerMaxReadFileLine = task.apiConfiguration?.maxReadFileLine
+					const result = this.processTextFile(fileContent, entry, providerMaxReadFileLine)
 
 					await task.fileContextTracker.trackFileContext(relPath, "read_tool" as RecordSource)
 
@@ -265,20 +266,30 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 
 	/**
 	 * Process a text file according to the requested mode.
+	 *
+	 * @param content - The raw file content
+	 * @param entry - The parsed file entry parameters
+	 * @param providerMaxReadFileLine - Optional provider-level cap on returned lines
 	 */
-	private processTextFile(content: string, entry: InternalFileEntry): string {
+	private processTextFile(content: string, entry: InternalFileEntry, providerMaxReadFileLine?: number): string {
 		const mode = entry.mode || "slice"
+		const defaultLimit = providerMaxReadFileLine ?? DEFAULT_LINE_LIMIT
 
 		if (mode === "indentation") {
 			// Indentation mode: semantic block extraction
 			// When anchor_line is not provided, default to offset (which defaults to 1)
 			const anchorLine = entry.anchor_line ?? entry.offset ?? 1
+			// Clamp the limit: if the provider has a max, enforce it even when the model requests more
+			const requestedLimit = entry.limit ?? defaultLimit
+			const effectiveLimit = providerMaxReadFileLine
+				? Math.min(requestedLimit, providerMaxReadFileLine)
+				: requestedLimit
 			const result = readWithIndentation(content, {
 				anchorLine,
 				maxLevels: entry.max_levels,
 				includeSiblings: entry.include_siblings,
 				includeHeader: entry.include_header,
-				limit: entry.limit ?? DEFAULT_LINE_LIMIT,
+				limit: effectiveLimit,
 				maxLines: entry.max_lines,
 			})
 
@@ -287,7 +298,6 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 			if (result.wasTruncated && result.includedRanges.length > 0) {
 				const [start, end] = result.includedRanges[0]
 				const nextOffset = end + 1
-				const effectiveLimit = entry.limit ?? DEFAULT_LINE_LIMIT
 				// Put truncation warning at TOP (before content) to match @ mention format
 				output = `IMPORTANT: File content truncated.
 	Status: Showing lines ${start}-${end} of ${result.totalLines} total lines.
@@ -306,7 +316,11 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 		// NOTE: read_file offset is 1-based externally; convert to 0-based for readWithSlice.
 		const offset1 = entry.offset ?? 1
 		const offset0 = Math.max(0, offset1 - 1)
-		const limit = entry.limit ?? DEFAULT_LINE_LIMIT
+		// Clamp the limit: if the provider has a max, enforce it even when the model requests more
+		const requestedSliceLimit = entry.limit ?? defaultLimit
+		const limit = providerMaxReadFileLine
+			? Math.min(requestedSliceLimit, providerMaxReadFileLine)
+			: requestedSliceLimit
 
 		const result = readWithSlice(content, offset0, limit)
 
@@ -786,8 +800,10 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 					}
 					content = selectedLines.join("\n")
 				} else {
-					// Read with default limits using slice mode
-					const result = readWithSlice(rawContent, 0, DEFAULT_LINE_LIMIT)
+					// Read with default limits using slice mode, clamped by provider setting
+					const providerMaxReadFileLine = task.apiConfiguration?.maxReadFileLine
+					const legacyLimit = providerMaxReadFileLine ?? DEFAULT_LINE_LIMIT
+					const result = readWithSlice(rawContent, 0, legacyLimit)
 					content = result.content
 					if (result.wasTruncated) {
 						content += `\n\n[File truncated: showing ${result.returnedLines} of ${result.totalLines} total lines]`

webview-ui/src/components/settings/ApiOptions.tsx

@@ -102,6 +102,7 @@ import { Verbosity } from "./Verbosity"
 import { TodoListSettingsControl } from "./TodoListSettingsControl"
 import { TemperatureControl } from "./TemperatureControl"
 import { RateLimitSecondsControl } from "./RateLimitSecondsControl"
+import { MaxReadFileLineControl } from "./MaxReadFileLineControl"
 import { ConsecutiveMistakeLimitControl } from "./ConsecutiveMistakeLimitControl"
 import { BedrockCustomArn } from "./providers/BedrockCustomArn"
 import { RooBalanceDisplay } from "./providers/RooBalanceDisplay"
@@ -786,6 +787,10 @@ const ApiOptions = ({
 									value={apiConfiguration.rateLimitSeconds || 0}
 									onChange={(value) => setApiConfigurationField("rateLimitSeconds", value)}
 								/>
+								<MaxReadFileLineControl
+									value={apiConfiguration.maxReadFileLine}
+									onChange={(value) => setApiConfigurationField("maxReadFileLine", value)}
+								/>
 								<ConsecutiveMistakeLimitControl
 									value={
 										apiConfiguration.consecutiveMistakeLimit !== undefined

webview-ui/src/components/settings/MaxReadFileLineControl.tsx

@@ -0,0 +1,41 @@
+import { useAppTranslation } from "@/i18n/TranslationContext"
+
+interface MaxReadFileLineControlProps {
+	value: number | undefined
+	onChange: (value: number | undefined) => void
+}
+
+export const MaxReadFileLineControl = ({ value, onChange }: MaxReadFileLineControlProps) => {
+	const { t } = useAppTranslation()
+
+	return (
+		<div className="flex flex-col gap-1">
+			<label className="block font-medium mb-1">{t("settings:providers.maxReadFileLine.label")}</label>
+			<div className="flex items-center gap-2">
+				<input
+					type="number"
+					className="w-24 bg-vscode-input-background text-vscode-input-foreground border border-vscode-input-border px-2 py-1 rounded text-right [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none"
+					value={value ?? ""}
+					min={1}
+					max={100000}
+					placeholder="2000"
+					onChange={(e) => {
+						const raw = e.target.value
+						if (raw === "") {
+							onChange(undefined)
+							return
+						}
+						const newValue = parseInt(raw, 10)
+						if (!isNaN(newValue) && newValue >= 1) {
+							onChange(newValue)
+						}
+					}}
+				/>
+				<span>{t("settings:providers.maxReadFileLine.unit")}</span>
+			</div>
+			<div className="text-sm text-vscode-descriptionForeground">
+				{t("settings:providers.maxReadFileLine.description")}
+			</div>
+		</div>
+	)
+}

webview-ui/src/i18n/locales/en/settings.json

@@ -598,6 +598,11 @@
 			"label": "Rate limit",
 			"description": "Minimum time between API requests."
 		},
+		"maxReadFileLine": {
+			"label": "Max file read lines",
+			"unit": "lines",
+			"description": "Maximum number of lines returned when reading a file. Lower values reduce prompt size and help slower providers avoid timeouts. Leave empty to use the default (2000)."
+		},
 		"consecutiveMistakeLimit": {
 			"label": "Error & Repetition Limit",
 			"description": "Number of consecutive errors or repeated actions before showing 'Roo is having trouble' dialog. Set to 0 to disable this safety mechanism (it will never trigger).",