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

Goes beyond the annotations by disclosing the required OAuth scope (newsletter:write) and by explaining the idempotency contract ('stable idempotency_key for this intended action; reuse it on retries'), which is genuinely useful for a retry-safe write. It stops short of explaining what the destructiveHint=true flag means in practice (e.g., whether options are replaced wholesale).

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 tight sentences, front-loaded with the action, then the auth/idempotency prerequisites, then the companion tool. No filler or restatement of the tool name.

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?

An output schema exists so return values need not be described, and the description covers the mutation, its auth scope, retry semantics and a related read tool. The remaining gap is the semantics of the update itself (merge vs replace on options, partial-update behavior).

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 0%, so the description must carry the burden. It clarifies label, options, and the retry semantics of idempotency_key, but leaves project_id and field_id unexplained and does not say whether label/options are partial-update fields or a full replacement.

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 and resource ('Update a custom field label or validation options'), naming the two mutable aspects. The final sentence routes to get_newsletter_schema, which cleanly separates this mutation tool from the schema/definition reader and from create_/list_ siblings.

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 implied (update an existing field rather than create one), and it points to get_newsletter_schema for definitions, but it gives no explicit when-to-use/when-not or alternatives among the many update_* siblings. The idempotency instruction is operational guidance rather than tool-selection guidance.

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