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kObsidian MCP

Update Marp Deck

marp.update
DestructiveIdempotent

Update a Marp deck by replacing a slide's body using slide ID or index, or merge fields into the deck's frontmatter. Idempotent operation that overwrites in place on the session-active vault.

Instructions

Mutate a Marp deck in place. part:'slide' replaces one slide's body (located by slideId or index) without touching neighbouring slides. part:'frontmatter' merges fields into the deck's frontmatter — unspecified fields are preserved; pass null to a field to unset it. Idempotent — re-running with identical inputs is a no-op on the file contents. Destructive — overwrites in place.

Operates on the session-active vault (see vault.current — selectable via vault.select) unless an explicit vaultPath argument is passed, which always wins.

Examples:

Example 1 — Replace the second slide's body:

{
  "part": "slide",
  "filePath": "Decks/launch.md",
  "index": 1,
  "source": "# New headline\n\nUpdated body"
}

Example 2 — Change the deck's theme and set a new title:

{
  "part": "frontmatter",
  "filePath": "Decks/launch.md",
  "fields": {
    "theme": "gaia",
    "title": "Launch plan"
  }
}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
changedYesTrue if the tool altered vault state on this call; false if it was a no-op.
targetYesThe path or identifier the tool acted on.
summaryYesShort human-readable summary of what happened.
Behavior5/5

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

Adds significant detail beyond annotations: mutation in place, two modes, idempotent (re-run is no-op), destructive (overwrites), merges frontmatter preserving unspecified fields, null to unset, vault context. No contradiction with annotations (destructiveHint=true, idempotentHint=true).

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?

Well-structured with section headers and examples. Slightly long but each part adds value. Could be trimmed slightly, but examples enhance usability.

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?

Covers all aspects: idempotency, destructiveness, vault context, two modes, parameter details, examples. Output schema exists so return values not needed. Complete for a mutation tool with no schema-defined params.

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

Parameters5/5

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

Input schema has no properties (0 params), so description carries full burden. It introduces all parameters (part, filePath, index, slideId, source, fields) with detailed behavior for each, including examples. Fully compensates for empty schema.

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?

Starts with 'Mutate a Marp deck in place' - clear verb+resource. Two distinct modes (slide and frontmatter) are explicitly defined, distinguishing it from the read-only sibling 'marp.read'.

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

Usage Guidelines4/5

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

Explains when to use each part mode (slide vs frontmatter) and mentions idempotent/destructive behavior. Provides examples. Lacks explicit 'when not to use' relative to sibling tools like 'notes.edit' or 'blocks.update', but the context of Marp decks is clear.

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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