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agent_spawn_many

Start several agent sessions at once, either one per prompt or N clones of one prompt, and return created and failed IDs so partial fan-out is visible.

Instructions

Start several sessions at once — one per prompt, or N clones of one prompt. Returns the ids it created and any that failed, so a partial fan-out is visible instead of silent.

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": {
      "harness": "<harness>"
    },
    "name": "agent_spawn_many"
  }
}

Input Schema

Name	Required	Description
`cwd`	No
`count`	No	If prompts is omitted, start this many clones of `prompt`
`model`	No
`effort`	No
`prompt`	No	Prompt used with count
`harness`	Yes
`prompts`	No	One session per prompt
`stagger_ms`	No	Gap between starts (default 800)
`name_prefix`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Oct 19, 2026

TDQS

A3.7/5.0

Behavior3/5

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

With no annotations, the description carries the full burden. It does disclose valuable behavior beyond the schema: partial fan-out returns both created ids and failures instead of failing silently. However it omits concurrency/rate limits, whether a failure aborts the remaining starts, and whether calls block until sessions are live.

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

Conciseness5/5

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

Two compact sentences, front-loaded with what the tool does, followed by the return contract. Every clause earns its place; nothing is restated from the schema.

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?

No output schema exists, and the description usefully covers the return shape (ids plus failures), which is the most important gap. But for a 9-parameter mutation tool with no annotations, the failure semantics, limits, and six undocumented parameters leave it short of complete.

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 44%, below the 50% threshold, so the description should compensate more than it does. It clarifies the tricky prompts-vs-count/prompt relationship, but cwd, model, effort, harness, stagger_ms, and name_prefix remain undocumented in both schema and description.

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 and resource ("Start several sessions at once") and immediately scopes the two operating modes, one-per-prompt vs N clones. Read against sibling agent_spawn, the plural/batch nature is unmistakable without opening either schema.

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 implies the usage context (fan-out when you need many sessions at once) but never states when to prefer this over repeatedly calling agent_spawn, nor any preconditions. Usage is inferable from the mode description rather than stated as guidance.

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