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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world write, so the safety profile is covered. The description adds a genuinely unannotated behavioral fact — that the account's plan caps the number of projects — plus the isolation semantics. It doesn't say what happens when the cap is hit, whether names must be unique, or that calling twice creates two projects (implied by idempotentHint=false but not stated).

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, front-loaded with the action, then definition, then usage, then constraint. No filler, though the plan-cap sentence is terse enough to raise a question (what cap, what happens at it) without answering it.

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 3-parameter, non-destructive creation tool with annotations and no output schema, the description covers what is created and the main governance constraint. It omits the return value (presumably the created project, including its id, which callers would need for follow-up calls) and any failure modes such as plan-limit rejection.

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 coverage is 67%: timezone and postal_address are well documented in the schema, including the consequence that a null address blocks marketing email. The description adds nothing about parameters, and name has no description in either place, but a minLength-1 string name is largely self-evident, so the baseline of 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?

"Create a project" supplies a specific verb and resource, and the following clause defines what a project actually is (an isolated space with its own contacts, campaigns, sender and settings), which distinguishes it from get_project, list_projects and update_project. An agent can tell what this tool makes without opening the schema.

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?

"Use one per product or brand" gives a concrete creation heuristic, and the plan-cap sentence flags a precondition worth checking. There is no explicit exclusion of alternatives (e.g. that changes afterwards go through update_project, or that list_projects shows existing ones), so it stops short of full when/when-not guidance.

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