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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds meaningful context beyond that: an authorization prerequisite and the fact that the call returns an error until projects are enabled for the account, which is behavior an agent cannot infer from annotations. It does not say whether inactive projects are silently excluded or how pagination works.

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 sentences, purpose front-loaded, then the returned-field inventory. The field enumeration is long but earns its place since there is no output schema. The parenthetical endpoint reference is the only minor clutter.

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?

With no output schema, listing the returned fields (id, api_key, name, country, send_enabled, counters, etc.) is the right completeness move, and the access precondition is stated. The remaining gap is filter behavior and whether inactive projects are included, minor for a two-optional-parameter read tool.

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 100% with both parameters documented, so the schema carries the semantics and baseline 3 applies. The description never mentions that the result can be narrowed by project_id or project_api_key, adding no meaning beyond the schema.

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 names the resource ("Active projects of the account") and the API endpoint (project/list), and enumerates the returned fields, so an agent knows exactly what is being retrieved. The 'active' qualifier even signals a scope restriction beyond the bare name. It stops short of a clean explicit verb phrase and doesn't contrast itself with siblings like get_account or list_domains.

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?

It provides a real precondition — an account key with projects enabled, otherwise the call errors — which tells the agent when the tool will fail. However, it gives no guidance on when to prefer this over create_project/update_project/delete_project, nor on how the optional filters change the result set.

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