Execute multiple tool calls in one request, optionally in parallel when all called tools are read-only. Combine related operations to reduce round trips while enforcing safety.
Run several tool calls in one request. Parallel mode is allowed only when every called tool is read-only.
| Name | Required | Description | Default |
|---|---|---|---|
| calls | Yes | ||
| parallel | No | ||
| stopOnError | No | ||
| failOnAnyError | No |
Changes observed during successful MCP inspections.
v1.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare destructiveHint=true and readOnlyHint=false, so the risk profile is known. The description adds the read-only precondition for parallel execution, which is useful. But it omits error-handling behavior (what stopOnError vs failOnAnyError actually do, especially with both defaulting to false) and the 20-call cap from 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.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two short sentences, front-loaded with what the tool does followed by the key constraint. No filler. It is terse to the point of under-specification, but that is a completeness problem rather than a verbosity one.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a meta-tool with 4 parameters, 0% schema description coverage, and no output schema, the description is thin. It should define batch entry structure, the 20-call ceiling, and the distinct roles of stopOnError/failOnAnyError to make the tool safely invocable. Annotations cover safety but not orchestration semantics.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0% across 4 parameters, so the description must compensate — and largely does not. Only the conditional meaning of 'parallel' is addressed; 'calls', 'stopOnError', and 'failOnAnyError' are never explained, and the maxItems:20 limit is not mentioned. This leaves the most consequential semantics undocumented.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
States a specific verb and resource: 'Run several tool calls in one request.' An agent immediately knows this is a multiplexer/batch executor, distinct from any single-call sibling. However, it does not clarify what a 'call' entry must contain (tool name + args) or how results are returned, leaving some ambiguity.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides one explicit usage rule: parallel mode is permitted only when every called tool is read-only. That is genuine guidance. But it says nothing about when to prefer batch over issuing calls individually, nor about how stopOnError/failOnAnyError affect execution, so the guidance is partial.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.