Caption File Check

caption_compare

Read-only

Compare exactly two caption or subtitle files under identical bounded checks: an original versus its translated track, before versus after a timing fix, or a format migration. Attach two WebVTT, SRT, or TTML/IMSC caption files in chat or give two publicly fetchable URLs and it runs the same SSRF-guarded, 2 MB-capped preflight as caption_check on each, then aligns them by cue index and reports side-by-side pass status, detected-format and encoding differences, the cue-count delta, timing drift and overlap differences, reading-speed (CPS) regressions, structural-error deltas, and a winner only when the measured checks separate the two. Use caption_check for a single file. It reports only source-file conformance, timing, encoding, and reading-speed facts against a dated profile: never translation quality, transcription accuracy, or sync against the video. Fetching and parsing two live files can take up to 60 seconds. WebVTT limitation: the parser drops payload-less cues; cue counts, indices, timing checks and comparisons cover retained cues only, not those omitted cues.

Input Schema

TableJSON Schema

Name	Required	Description
`urls`	No	Exactly two public caption URLs to compare, in the order they should appear side by side (for example original then translated). Provide either this or files, never both. STRICT RULE: Caption compare failed — provide either two caption URLs or two attached caption files, not both STRICT RULE: Caption compare failed — provide two public caption URLs or attach two caption files
`files`	No	Exactly two caption files attached in chat to compare, in the order they should appear side by side (for example original then translated). Provide either this or urls, never both.
`profile`	No	Named reading-speed profile applied to both tracks. netflix-adult-20 (default), netflix-children-17, youtube, ebu-tt.

Output Schema

TableJSON Schema

Name	Required	Description
`notes`	Yes	Notes about incomplete checks or completion under identical limits
`tracks`	Yes	The two tracks in input order
`winner`	No	Track with fewer weighted structural, timing, reading-speed, and line-length problems
`profile`	Yes	Reading-speed and line-length profile applied to the caption checks
`checkedAt`	Yes	ISO timestamp when the caption result was produced
`comparison`	No	Measured differences between the two successfully preflighted tracks

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 10, 2026

TDQS

A4.7/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnlyHint/destructiveHint annotations, the description discloses SSRF-guarded and 2 MB-capped fetching, a 60-second execution bound, and a WebVTT parser limitation (payload-less cues are dropped). It also clarifies that only source-file conformance facts are reported, adding significant behavioral context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core purpose, then flows through input modes, behavior, output highlights, exclusions, performance, and limitations. Every sentence carries necessary information with no redundancy or filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a comparison tool with two input modes, a profile parameter, an output schema, and meaningful edge cases, the description covers all critical operational details: preflight constraints, alignment method, reported metrics, timing, exclusions, and known parser limitations. An agent has everything needed to invoke it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the input schema already fully documents urls, files, and profile including the strict mutual-exclusion rule. The description adds no parameter-specific meaning beyond what the schema provides, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource ('Compare exactly two caption or subtitle files') and immediately enumerates concrete use cases (original vs. translated, before vs. after timing fix, format migration). It also names the sibling tool caption_check, making the distinction unmistakable.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly directs agents with 'Use caption_check for a single file,' establishing when this tool applies versus the sibling. It further states what the tool does NOT do ('never translation quality, transcription accuracy, or sync against the video'), which prevents misuse.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All Caption File Check tools Inspect

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