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

The description says 'Register' but does not clarify if this is a safe read-only operation or a mutating one. The name 'create' implies mutation, but without annotations, the description should disclose side effects, authentication requirements, or whether registrations are permanent. It misses the opportunity to state it requires an API key (which is in schema) or any billing implications.

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 description is concise and to the point, with a single sentence that is front-loaded. It does not waste words on fluff, but it might be slightly under-specified given the tool's complexity, so a 4 is fitting rather than 5.

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?

The tool has 8 parameters with no output schema and no annotations, yet the description provides minimal guidance on the operation's outcome or behavior. It fails to define the purpose of parameters like api_key, proxy_slug, and upstream_url beyond what the schema implies. For a complex tool that creates a new server, the description is too brief to guide an agent effectively.

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?

Since the schema describes all 8 parameters (100% coverage), the description doesn't need to duplicate them. However, it adds no extra meaning about how parameters interact, such as that transport and auth_mode have defaults, or that proxy_slug must be unique. With full schema coverage, a baseline of 3 is appropriate as the description adds no added value 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 'Register a new MCP server for billing' clearly states the action (register/create) and resource (MCP server), with the context of billing. It is distinct from siblings like create_plan which creates a plan, and update_server which modifies an existing server. However, it doesn't explicitly mention alternatives like update_server for modifications, so a small deduction from a perfect 5.

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?

There is no guidance on when to use this tool versus alternatives. The description does not mention that this is for creating a new server, while update_server is for modifying an existing one, or that register_operator is for registering operators first. The agent must infer usage from the tool name alone, which lacks the clarity of explicit instructions.

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