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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=false, so the mutation profile is covered. The description adds value beyond that by stating the return value (the new project id), that ownership is bound to the signed-in user, and that plan quotas can block creation — a real failure mode an agent should anticipate. It stops short of saying what happens on quota exhaustion (error shape, upgrade path).

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?

Three short sentences with zero padding: purpose and ownership first, return value second, constraint third. Nothing is repeated from the schema and every sentence carries information.

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 two-parameter creation tool with no output schema, the description covers purpose, return value, ownership scope, and the quota constraint — enough to call it correctly. The only remaining gap is failure behavior when a plan limit is hit, which is a minor omission.

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 100%, so 'name' and 'description' are already documented in the schema with length bounds. The description adds no additional parameter meaning, so the baseline 3 applies.

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?

The description opens with a specific verb and resource ('Create a new MagicPixel project') and adds ownership scope ('owned by the signed-in user'), so an agent knows exactly what the tool produces. It does not explicitly contrast itself with siblings such as create_folder or list_projects, so it stops short of full sibling differentiation.

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?

Usage is only implied by the verb; there is no explicit 'use this when...' guidance or pointer to alternatives like list_projects for reading existing projects. The plan-limit sentence ('1 project on free/hobby, more on paid plans') is a genuinely useful precondition that tells the agent creation can fail, which lifts it above a bare 2.

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