cozyvtt-mcp

Character Update

character_update

Destructive

Update an existing character sheet with a partial patch, preserving all unspecified fields. Provide only name, data, or tokenImageUrl; nested data merges recursively.

Instructions

Patch an existing sheet while preserving unspecified fields (owner or campaign DM). Use character_get first; use token_hp_update for a signed HP change and character_create for a new sheet. data is a request-field object, e.g. {"data":{"hp":{"current":5}}}. Only name/data/tokenImageUrl are allowed at the top level. Nested data dictionaries merge recursively after a GET; arrays/scalars replace whole values and null is an explicit value, not deletion. The caller calculates rules values using the sheet's own gameSystem. Updates are locked only within this process; concurrent browser saves may be lost. Reapplying values is stable absent concurrent edits, but upstream update side effects are not guaranteed idempotent. REST errors retain diagnostics. Returns {ok:true,data} on success; tool-body failures return {ok:false,error} with optional diagnostic data. Argument-schema errors are MCP errors.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`data`	Yes	Nonempty request patch containing only name, data, tokenImageUrl. Sheet changes go inside data as an object; arrays replace, null is explicit.
`character_id`	Yes	Existing sheet ID to modify; upstream enforces owner or campaign DM access.

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.3.0Sep 20, 2026

addedInput schema / properties / character_id / description

Added value: +"Existing sheet ID to modify; upstream enforces owner or campaign DM access."

addedInput schema / properties / data / description

Added value: +"Nonempty request patch containing only name, data, tokenImageUrl. Sheet changes go inside data as an object; arrays replace, null is explicit."

First observedv0.1.0Sep 5, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Annotations already flag destructive and non-idempotent behavior, but the description adds substantial context: merge semantics, null-as-explicit-value, concurrency limits, potential loss of concurrent browser saves, and error/response shapes. This goes well beyond what annotations alone provide and does not contradict them.

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?

The description is dense and front-loaded with the main purpose, but it is long and somewhat repetitive with the schema's parameter descriptions. Every sentence adds real behavioral value, though restructuring into clearer sections would improve scannability.

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 mutating patch tool with nested objects and concurrency caveats, the description is unusually complete: it covers access constraints, merge rules, idempotency, error behavior, and return shapes. The presence of an output schema further reduces the burden, so nothing essential is missing.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds a concrete example, restricts top-level fields to name/data/tokenImageUrl, and clarifies nested merge behavior. This meaningfully supplements the schema even though the schema already carries solid parameter descriptions.

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: 'Patch an existing sheet while preserving unspecified fields.' It also distinguishes itself from siblings by explicitly routing to character_get, token_hp_update, and character_create, so an agent can tell this tool apart without opening schemas.

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?

It gives explicit when-to-use guidance: use character_get first, use token_hp_update for a signed HP change, and use character_create for a new sheet. It also clarifies caller responsibility for computing rule values, which helps the agent decide whether this is the right tool.

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