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

With only destructiveHint=true provided, the description adds meaningful context: the operation is additive, it triggers no outbound message, contacts are unique by email (implying duplicate handling), and it names the underlying endpoint. There is mild tension with destructiveHint=true since "additive" under MCP semantics aligns with a non-destructive hint, but the term reads as "inserts a new record / sends nothing" rather than a read-only claim.

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, front-loaded clauses with zero filler. The identifying purpose, the behavioral note, and the API path are each packed into a single sentence and nothing is repeated.

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 single-record create tool with no output schema, the description covers purpose, side-effect profile, uniqueness, and endpoint, which is nearly enough to call it confidently. It stops short of noting what is returned (e.g., the created contact id) or how duplicate-email conflicts surface, which a mutation with no output schema could benefit from.

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%, including the nested "data" object and its property-creation dependency, so the schema already documents all five parameters. The description only restates the email uniqueness constraint that the schema also notes, adding no new parameter semantics. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

States a specific verb+resource ("Creates a contact (CRM record) in Bird") and even names the API endpoint (POST /v1/contacts). The clause "additive, sends no message" distinguishes it from the messaging siblings in the same server, so an agent can place it 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?

The description implies usage (create a CRM contact) and clarifies it does not send a message, which nudges against the sibling messaging/audience tools. However, it never states when to use this over bird_get_contact or bird_create_audience, nor any prerequisite like verifying the contact doesn't already exist.

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