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by io.github.jakehandy
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Change somebody in a battle

update_participant

Their name, side, initiative, stat block or state. Health for a character at this table lands on their own sheet. GM only. Returns: The battle.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "campaign": "<campaign>",
      "battle": "<battle>",
      "participant": "<participant>"
    },
    "name": "update_participant"
  }
}

Input Schema

NameRequiredDescriptionDefault
nameNoTheir name.
roleNoA short line under the name.
sideNoWhich way they point.
stateNoHealth and the GM's notes. For a character at this table, health is written to their own sheet.
statsNoA stat block you supply, for somebody nobody has a sheet for. Invent it or take it from your own notes.
battleYesThe battle's id.
controlNoWho runs them.
campaignYesThe campaign, by its slug (what its link says) or its id.
initiativeNoTheir initiative total, with the bonus already in. Stored exactly as given.
participantYesThe participant's id.
initiativeRollNoOr the number on the die alone: their bonus is added for you (a character's live one off their sheet). Wins over `initiative`.
initiativeBonusNoTheir bonus, which breaks ties. Never added to `initiative`.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • changedInput schema / properties / initiative / description
      Previous value: -"What they rolled."New value: +"Their initiative total, with the bonus already in. Stored exactly as given."
    • changedInput schema / properties / initiativeBonus / description
      Previous value: -"Their bonus."New value: +"Their bonus, which breaks ties. Never added to `initiative`."
    • addedInput schema / properties / initiativeRoll
      Added value: +{
+  "description": "Or the number on the die alone: their bonus is added for you (a character's live one off their sheet). Wins over `initiative`.",
+  "type": "integer"
+}
  2. First observed

TDQS

B3/5.0
Behavior4/5

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

Beyond the annotations (readOnly=false, destructive=false, idempotent=false), the description discloses two things structured data does not: an authorization requirement ('GM only') and a non-obvious side effect ('Health for a character at this table lands on their own sheet'), plus the return value. It stops short of stating that unspecified fields are left untouched or what happens if the participant id is unknown.

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

Conciseness3/5

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

It is short and front-loaded, but the telegraphic style costs clarity: 'Their name, side...' has no subject and Health/stat-block placement notes compete with the field list. Every sentence earns its place, yet the fragment form is under-specified rather than tight.

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

Completeness3/5

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

For a 12-parameter nested mutation tool with no output schema, the description covers auth, one side effect and the return value, but leaves merge/patch behavior, error cases and the character-vs-NPC distinction (where the 'state' health is written) to be inferred from the schema alone.

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 coverage is 100% and the schema descriptions are unusually rich (initiativeRoll 'Wins over `initiative`', initiativeBonus 'Never added to `initiative`'), so the baseline is 3. The description's 'or' hints at partial-update semantics and lists name/side/initiative/stats/state, but omits role, control, initiativeRoll and initiativeBonus entirely.

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

Purpose3/5

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

The body is a fragment ('Their name, side, initiative, stat block or state') that only makes sense once paired with the title 'Change somebody in a battle'. It lists the mutable fields, so an agent can infer a partial update of a battle participant, but it never states the verb+resource outright and does nothing to separate itself from siblings like change_participant_health or update_character_state.

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

Usage Guidelines2/5

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

The only routing guidance is the precondition 'GM only'. Nothing says when to use this instead of change_participant_health for hit points, update_companion for companions, or update_character_state for sheet state — all plausible-looking alternatives in the sibling list. Usage must be inferred from the field list.

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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