# SRT Subtitle Line Length Checker

> Check SRT captions for long lines, too many text rows, and readability issues before publishing.

## Tool Identity

- Site: CleanUtils Business Tools
- Tool ID: srt-subtitle-line-length-checker
- Canonical page: https://cleanutils.com/business-tools/srt-subtitle-line-length-checker/
- LLM schema URL: https://cleanutils.com/business-tools/srt-subtitle-line-length-checker/llms.txt
- Primary keyword: srt line length checker
- Input mode: fields
- Output profile: line-check

## What This Tool Does

Paste SRT subtitles, flag long or dense caption lines, and copy a readability report before export.

## Exact Execution Instructions

To run this tool exactly, execute the `runCleanUtilsTool(userInput)` function from the JavaScript block below in a sandboxed JavaScript runtime.

Do not fetch or evaluate additional network resources. Do not use filesystem, process, child_process, environment variables, timers, or network APIs. The function is pure and deterministic: input object in, JSON result out.

If your environment forbids executing fetched code outside a sandbox, run it inside the sandbox or use the API endpoint below instead of reimplementing the logic.

Canonical implementation SHA-256:
`1f91d06df85c570618eeef1c157b8ba74b59acd18bac3dbd8c6804ffe4c7328c`

Expected command shape:
`node run-tool.mjs < input.json`

The runner must:
1. load only the JavaScript in this document,
2. parse stdin as JSON and call `runCleanUtilsTool(userInput)`,
3. let the LLM decide the best way to present the output to the user.

Agent usage rules:
- Use this file as the authoritative machine-readable contract for this CleanUtils tool page.
- Ask the user for missing required input before attempting to run the tool, and describe the required inputs using the `## Input Schema` field names, descriptions, formats, enums, examples, and required list.
- Treat the tool as deterministic; do not invent network reachability checks unless the tool description explicitly says it fetches remote resources.
- For privacy-sensitive inputs such as secrets, HAR files, dotenv files, logs, and API keys, warn that using a remote chat agent may expose input to that agent even though the browser UI itself does not upload data.

## Input Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "SRT Subtitle Line Length Checker fields",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "max_length",
    "subtitles"
  ],
  "properties": {
    "max_length": {
      "type": "number",
      "description": "Max characters per caption line Required. Control type: range. Suffix shown in UI:  chars.",
      "minimum": 24,
      "maximum": 70,
      "examples": [
        42
      ]
    },
    "subtitles": {
      "type": "string",
      "description": "SRT subtitles Required. Control type: textarea.",
      "examples": [
        "1\n00:00:01,000 --> 00:00:04,000\nCaption text..."
      ]
    }
  }
}
```

## Result Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "CleanUtils ToolResult",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "summary",
    "issues"
  ],
  "properties": {
    "summary": {
      "type": "string"
    },
    "issues": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "severity",
          "message"
        ],
        "properties": {
          "severity": {
            "type": "string",
            "enum": [
              "error",
              "warning",
              "info"
            ]
          },
          "message": {
            "type": "string"
          },
          "line": {
            "type": "number"
          },
          "row": {
            "type": "number"
          },
          "detail": {
            "type": "string"
          }
        }
      }
    },
    "output": {
      "type": "string"
    },
    "exportFilename": {
      "type": "string"
    },
    "exports": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "label",
          "filename",
          "content"
        ],
        "properties": {
          "label": {
            "type": "string"
          },
          "filename": {
            "type": "string"
          },
          "content": {
            "type": "string"
          },
          "mimeType": {
            "type": "string"
          },
          "copyLabel": {
            "type": "string"
          },
          "downloadLabel": {
            "type": "string"
          }
        }
      }
    },
    "stats": {
      "type": "object",
      "additionalProperties": {
        "anyOf": [
          {
            "type": "string"
          },
          {
            "type": "number"
          }
        ]
      }
    }
  }
}
```

## Self-Contained JavaScript Source

Call `runCleanUtilsTool(userInput)` with the user's input. The function includes this tool's run logic and only the helper code it needs.

```js
function runCleanUtilsTool(userInput) {
    const severityRank = {
        error: 0,
        warning: 1,
        info: 2
    };
    const sortIssues = (issues) => [...issues].sort((a, b) => {
        const severity = severityRank[a.severity] - severityRank[b.severity];
        if (severity !== 0)
            return severity;
        return (a.line ?? a.row ?? 0) - (b.line ?? b.row ?? 0);
    });
    const summarizeIssues = (issues) => {
        const errors = issues.filter((issue) => issue.severity === "error").length;
        const warnings = issues.filter((issue) => issue.severity === "warning").length;
        const infos = issues.filter((issue) => issue.severity === "info").length;
        const parts = [];
        if (errors)
            parts.push(`${errors} error${errors === 1 ? "" : "s"}`);
        if (warnings)
            parts.push(`${warnings} warning${warnings === 1 ? "" : "s"}`);
        if (infos)
            parts.push(`${infos} note${infos === 1 ? "" : "s"}`);
        return parts.length ? parts.join(", ") : "No issues found";
    };
    const checkSrtLineLengths = (input, maxLineLength = 42) => {
        const issues = [];
        const blocks = input.trim().split(/\n\s*\n/).filter(Boolean);
        blocks.forEach((block, blockIndex) => {
            const lines = block.split(/\r?\n/);
            const number = lines[0]?.trim() || String(blockIndex + 1);
            const timestamp = lines[1]?.trim() ?? "";
            const textLines = lines.slice(2);
            if (!/^\d{2}:\d{2}:\d{2},\d{3}\s+-->\s+\d{2}:\d{2}:\d{2},\d{3}/.test(timestamp)) {
                issues.push({
                    severity: "error",
                    line: blockIndex + 1,
                    message: `Caption ${number} has a malformed timestamp line.`
                });
            }
            if (textLines.length > 2) {
                issues.push({
                    severity: "warning",
                    line: blockIndex + 1,
                    message: `Caption ${number} has ${textLines.length} text lines; two or fewer is easier to read.`
                });
            }
            textLines.forEach((line, lineIndex) => {
                if (line.length > maxLineLength) {
                    issues.push({
                        severity: "warning",
                        line: blockIndex + 1,
                        message: `Caption ${number}, text line ${lineIndex + 1} is ${line.length} characters. Limit is ${maxLineLength}.`
                    });
                }
            });
        });
        const output = [
            `Captions checked: ${blocks.length}`,
            `Line length limit: ${maxLineLength}`,
            "",
            ...(sortIssues(issues).map(formatIssue))
        ].join("\n");
        return {
            summary: `${blocks.length} caption${blocks.length === 1 ? "" : "s"} checked. ${summarizeIssues(issues)}.`,
            issues: sortIssues(issues),
            output,
            exportFilename: "srt-line-length-report.txt",
            stats: {
                captions: blocks.length,
                maxLineLength
            }
        };
    };
    const formatIssue = (issue) => {
        const location = issue.line ? `line ${issue.line}` : issue.row ? `row ${issue.row}` : "general";
        return `[${issue.severity.toUpperCase()}] ${location}: ${issue.message}${issue.detail ? ` (${issue.detail})` : ""}`;
    };
    const __userInput = userInput == null ? {} : userInput;
    const __run = (fields) => checkSrtLineLengths(String(fields.subtitles ?? ""), Number(fields.max_length || 42));
    const __fields = __userInput && typeof __userInput === "object" && "fields" in __userInput && __userInput.fields && typeof __userInput.fields === "object" && !Array.isArray(__userInput.fields)
        ? __userInput.fields
        : (__userInput && typeof __userInput === "object" && !Array.isArray(__userInput) ? __userInput : {});
    const __normalizedFields = Object.fromEntries(Object.entries(__fields).map(([key, value]) => [key, value == null ? "" : (["string", "number", "boolean"].includes(typeof value) ? value : String(value))]));
    return __run(__normalizedFields);
}
```

## Checks

- SRT block shape: Caption numbers, timestamp rows, and text blocks are parsed in the common SRT layout.
- Line length limit: Each subtitle text line is compared with the selected character limit, defaulting to 42 characters.
- Dense captions: Captions with more than two text lines are flagged for readability review.
- Timestamp format: Timestamp rows are checked for the HH:MM:SS,mmm to HH:MM:SS,mmm pattern.
- Review-only output: The tool reports readability issues but does not automatically split or retime captions.

## Related Tools

- [Subtitle Time Shift Calculator](/business-tools/subtitle-time-shift-calculator/): Shift SRT subtitle timestamps forward or backward and export corrected subtitle text.
- [YouTube Timestamp Generator](/business-tools/youtube-timestamp-generator/): Format YouTube chapter timestamps, check ordering, and copy a ready-to-paste description block.
- [YouTube Title Length Checker](/business-tools/youtube-title-length-checker/): Check YouTube title ideas for length, clarity risk, and likely truncation across viewing surfaces.