Premiere Pro MCP Server

Build Caption Artifact

build_caption_artifact

Builds CapCut-style SRT or VTT caption files from a word-timed transcript, with balanced cue grouping, sentence-aware breaks, karaoke timestamps, and emphasis or speaker markup. Writes locally without changing Premiere.

Instructions

Build a CapCut/Submagic-style SRT or VTT caption artifact from a caller-supplied word timeline: balanced word groups, sentence-aware breaks, min/max cue durations, optional karaoke word timestamps (VTT), emphasis and speaker markup. Local-only; returns the artifact inline or writes it inside an approved workspace and never changes Premiere.

Input Schema

Name	Required	Description
`format`	Yes	Artifact format. SRT uses HH:MM:SS,mmm; VTT starts with WEBVTT and uses HH:MM:SS.mmm.
`karaoke`	No	VTT only: emit per-word <HH:MM:SS.mmm> timestamps inside each cue for word-highlight styles. Errors for SRT.
`max_lines`	No	Maximum lines of plain caption text per cue (default 1); markup does not add lines.
`uppercase`	No	Render caption text in upper case.
`output_path`	No	Optional absolute file path to write the artifact to. Requires approved_workspace_path; the file must not already exist. When omitted the artifact text is returned inline (up to 512 KiB).
`style_preset`	No	Style descriptor to return with the artifact (default clean). Documentation only; not encoded in SRT/VTT.
`strip_fillers`	No	Tokens removed from the caption text (case-insensitive, punctuation ignored).
`word_timeline`	Yes	Caller-supplied word-timed transcript for one Premiere source item. Words must be ordered by start time and bound to the transcript revision returned by get_clip_transcript_uxp. Different labeled speakers may overlap; same-speaker words may not, even when another speaker is between them.
`words_per_cue`	No	Target words per cue (default 4); sentences are split into balanced groups of at most this many words.
`emphasis_words`	No	Words wrapped in <b> (SRT) or <c.emphasis> (VTT).
`speaker_prefix`	No	Prefix cues with the speaker label when present: 'Speaker: ' in SRT, <v Speaker> in VTT.
`idempotency_key`	No	Optional client-chosen key (1-128 chars of A-Z a-z 0-9 . _ : -) for this intended edit. Pass a fresh key per edit and reuse it only when retrying that same edit, for example after a client-side timeout. A repeat with the same tool, key and arguments is not run again: while the first call is running it fails with IDEMPOTENCY_IN_PROGRESS (poll get_last_operations); after it finished it returns the original outcome marked replayed. A definite failure with nothing applied (receipt outcome not_applied) may be retried with the same key. Reusing a key with different arguments fails with IDEMPOTENCY_KEY_REUSED. Scoped to this MCP session (the stdio server process or one HTTP session) and held in memory only (200 keys, 1 hour); it does not survive a restart or reconnect. Read-only invocations are never deduplicated.
`max_cue_seconds`	No	Maximum cue duration (default 5).
`min_cue_seconds`	No	Minimum cue duration (default 0.5); short cues are extended but never past the next cue start.
`merge_gap_seconds`	No	Extend a cue to the next cue start when the gap is smaller than this (default 0.3) so captions do not flicker.
`max_chars_per_line`	No	Maximum characters per line of plain caption text (default 32); words are never split. Wrapping counts unescaped words only, so VTT escaping, karaoke timestamps, emphasis tags, and speaker prefixes can make the rendered line longer.
`expected_cep_target`	No	Optional reviewed CEP sequence/clip identity and exact tick ranges. Checked before every generated command; UXP refuses this CEP-only guard.
`expected_project_path`	No	Optional absolute saved-project path. Every generated CEP command refuses before its body when the active project differs or is unsaved. UXP commands refuse this CEP-only guard; local-only tools do not inspect Premiere. Omit to keep existing behavior.
`approved_workspace_path`	No	Absolute existing directory that must contain output_path (checked via realpath of the parent directory). Required with output_path.

Output Schema

Name	Required	Description
`ok`	Yes	Whether the tool completed successfully.
`data`	No	Tool-specific result data when ok is true; on failure, diagnostic detail when the tool provides it.
`tool`	Yes	The registered MCP tool name.
`error`	No	Failure detail when ok is false.
`receipt`	No	Versioned common mutation receipt; success never implies rendered verification.
`idempotency`	No	Present when idempotency_key deduplicated this call: replayed is true when the original outcome was returned instead of running again.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv1.25.0Oct 24, 2026

addedInput schema / properties / idempotency_key

Added value: +{
+  "description": "Optional client-chosen key (1-128 chars of A-Z a-z 0-9 . _ : -) for this intended edit. Pass a fresh key per edit and reuse it only when retrying that same edit, for example after a client-side timeout. A repeat with the same tool, key and arguments is not run again: while the first call is running it fails with IDEMPOTENCY_IN_PROGRESS (poll get_last_operations); after it finished it returns the original outcome marked replayed. A definite failure with nothing applied (receipt outcome not_applied) may be retried with the same key. Reusing a key with different arguments fails with IDEMPOTENCY_KEY_REUSED. Scoped to this MCP session (the stdio server process or one HTTP session) and held in memory only (200 keys, 1 hour); it does not survive a restart or reconnect. Read-only invocations are never deduplicated.",
+  "maxLength": 128,
+  "minLength": 1,
+  "pattern": "^[A-Za-z0-9._:-]+$",
+  "type": "string"
+}

addedOutput schema / properties / idempotency

Added value: +{
+  "additionalProperties": true,
+  "description": "Present when idempotency_key deduplicated this call: replayed is true when the original outcome was returned instead of running again.",
+  "type": "object"
+}

Changed3 schema fields changedv1.24.0Oct 12, 2026

addedInput schema / properties / expected_cep_target

Added value: +{
+  "additionalProperties": false,
+  "anyOf": [
+    {
+      "required": [
+        "sequence_id"
+      ]
+    },
+    {
+      "required": [
+        "source_item"
+      ]
+    }
+  ],
+  "description": "Optional reviewed CEP sequence/clip identity and exact tick ranges. Checked before every generated command; UXP refuses this CEP-only guard.",
+  "properties": {
+    "backend": {
+      "const": "cep",
+      "description": "Backend namespace for these IDs.",
+      "type": "string"
+    },
+    "clip": {
+      "additionalProperties": false,
+      "description": "Optional exact reviewed timeline clip.",
+      "properties": {
+        "effect": {
+          "additionalProperties": false,
+          "description": "Reviewed effect and parameter identity checked before mutation.",
+          "properties": {
+            "display_name": {
+              "description": "Optional exact host display name.",
+              "maxLength": 512,
+              "minLength": 1,
+              "type": "string"
+            },
+            "match_name": {
+              "description": "Effect match name from host inspection.",
+              "maxLength": 512,
+              "minLength": 1,
+              "type": "string"
+            },
+            "parameter_index": {
+              "description": "Inspected zero-based parameter index.",
+              "maximum": 255,
+              "minimum": 0,
+              "type": "integer"
+            },
+            "parameter_name": {
+              "description": "Exact inspected parameter name.",
+              "maxLength": 512,
+              "minLength": 1,
+              "type": "string"
+            }
+          },
+          "required": [
+            "match_name",
+            "parameter_index",
+            "parameter_name"
+          ],
+          "type": "object"
+        },
+        "end_ticks": {
+          "description": "Exact expected exclusive timeline end ticks.",
+          "pattern": "^-?\\d{1,30}$",
+          "type": "string"
+        },
+        "in_ticks": {
+          "description": "Exact expected source In ticks.",
+          "pattern": "^-?\\d{1,30}$",
+          "type": "string"
+        },
+        "node_id": {
+          "description": "Stable CEP node ID.",
+          "maxLength": 512,
+          "minLength": 1,
+          "type": "string"
+        },
+        "out_ticks": {
+          "description": "Exact expected exclusive source Out ticks.",
+          "pattern": "^-?\\d{1,30}$",
+          "type": "string"
+        },
+        "project_item_id": {
+          "description": "Expected source project-item node ID.",
+          "maxLength": 512,
+          "minLength": 1,
+          "type": "string"
+        },
+        "start_ticks": {
+          "description": "Exact expected timeline start ticks.",
+          "pattern": "^-?\\d{1,30}$",
+          "type": "string"
+        },
+        "track_index": {
+          "description": "Expected zero-based track index; identity still checked.",
+          "maximum": 255,
+          "minimum": 0,
+          "type": "integer"
+        },
+        "track_type": {
+          "description": "Expected media track group.",
+          "enum": [
+            "video",
+            "audio"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "node_id",
+        "track_type",
+        "track_index"
+      ],
+      "type": "object"
+    },
+    "project_document_id": {
+      "description": "Exact Premiere project document ID observed during review.",
+      "maxLength": 512,
+      "minLength": 1,
+      "type": "string"
+    },
+    "sequence_id": {
+      "description": "Stable expected active sequence ID.",
+      "maxLength": 512,
+      "minLength": 1,
+      "type": "string"
+    },
+    "source_item": {
+      "additionalProperties": false,
+      "description": "Reviewed source identity for a source-only operation.",
+      "properties": {
+        "media_path": {
+          "description": "Optional exact source-media path.",
+          "maxLength": 4096,
+          "minLength": 1,
+          "type": "string"
+        },
+        "node_id": {
+          "description": "Exact project-item node ID.",
+          "maxLength": 512,
+          "minLength": 1,
+          "type": "string"
+        }
+      },
+      "required": [
+        "node_id"
+      ],
+      "type": "object"
+    }
+  },
+  "required": [
+    "backend"
+  ],
+  "type": "object"
+}

addedInput schema / properties / expected_project_path

Added value: +{
+  "description": "Optional absolute saved-project path. Every generated CEP command refuses before its body when the active project differs or is unsaved. UXP commands refuse this CEP-only guard; local-only tools do not inspect Premiere. Omit to keep existing behavior.",
+  "maxLength": 4096,
+  "minLength": 1,
+  "type": "string"
+}

addedOutput schema / properties / receipt

Added value: +{
+  "additionalProperties": true,
+  "description": "Versioned common mutation receipt; success never implies rendered verification.",
+  "type": "object"
+}

Changed1 schema field changedv1.18.6Sep 30, 2026

changedOutput schema / properties / data / description

Previous value: -"Tool-specific result data when ok is true."New value: +"Tool-specific result data when ok is true; on failure, diagnostic detail when the tool provides it."

Changed1 schema field changedv1.16.0Sep 16, 2026

changedInput schema / properties / word_timeline / description

Previous value: -"Caller-supplied word-timed transcript for one Premiere source item. Words must be ordered by start time and bound to the transcript revision returned by get_clip_transcript_uxp."New value: +"Caller-supplied word-timed transcript for one Premiere source item. Words must be ordered by start time and bound to the transcript revision returned by get_clip_transcript_uxp. Different labeled speakers may overlap; same-speaker words may not, even when another speaker is between them."

Addedv1.14.9Sep 8, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations mark this as non-read-only but non-destructive, and the description supplies the missing context: it is local-only, never touches Premiere, and either returns text inline or writes to an approved workspace. That materially clarifies the blast radius. It stays silent on idempotency behavior and overwrite rules, which live only in the schema.

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

Conciseness4/5

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

Two sentences, front-loaded with the action and output type, no filler. The second sentence is a dense feature list, which is informative but reads compressed rather than structured.

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

Completeness4/5

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

Given 19 parameters, nested objects, and an output schema, the description covers purpose, output modes, and side effects adequately. It omits the idempotency and CEP-guard semantics needed for retry-safety, but those are documented in the schema.

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 parameter meanings are already fully documented, and the description largely restates them (word groups, min/max cue durations, karaoke, emphasis, speaker markup). It adds no syntax or format detail beyond the schema, 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?

States a specific verb (build) plus resource (SRT/VTT caption artifact), and names the input source (caller-supplied word timeline) and feature set (word groups, karaoke, emphasis, speaker markup). This clearly separates it from siblings such as retime_caption_file or read_sequence_captions.

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

Usage Guidelines3/5

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

The description establishes scope ('Local-only ... never changes Premiere') and the precondition of a caller-supplied word timeline, which implies when to use it. However, it never names an alternative tool or an explicit when-not condition, so the agent must infer routing against the many caption-adjacent siblings.

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

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