create_thread

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

Goes well beyond the annotations by disclosing approval requirements, idempotent behavior on request_id reuse, and the possibility that a failed/unknown operation may still have created a thread. It also clarifies model/sandbox defaults and the need to verify Desktop association, all without contradicting readOnlyHint=false or destructiveHint=true.

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?

The key purpose is front-loaded and every sentence adds a meaningful caveat, but a few phrases are cryptic (e.g., 'Approval policy is never') and could be clearer without adding length.

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 7-parameter mutation tool with rich side effects, the description covers when to use it, what it does not create, idempotency, failure ambiguity, approval, and return-value caveats. The output schema supplies the return details, so the remaining gaps are minor.

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%, but the description compensates for most parameters: cwd must exist, prompt is optional/initial, model/reasoning fall back to defaults, request_id is reusable/idempotent, and app_server_project_id must not be a Desktop saved-project ID. A few parameter details (title and request_id origin/format) remain implicit, preventing a 5.

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?

Opens with a specific verb-plus-resource: 'Create a retained session in an existing cwd, optionally with an initial prompt.' It distinguishes itself from the sibling worktree tool by explicitly stating 'No worktree or persistent Goal is created.'

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?

Gives clear context for use (existing cwd, retained session, no worktree/goal) and important invocation constraints (App Server project ID only, never Desktop saved-project ID). It does not explicitly name when to prefer create_worktree_thread or other siblings, relying instead on the exclusion clause.

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