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

With no annotations provided, the description carries the behavioral disclosure burden. It discloses the merge semantics (only provided keys updated), the return value (updated user summary), and the instance targeting behavior. While it does not cover permissions or reversibility, it provides meaningful behavioral context beyond the schema.

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 compact and front-loaded with the primary action and key scope ('Merge metadata fields... Only the provided metadata keys are updated'). Every sentence adds value, including the prerequisite call and the return type, with no filler or redundancy.

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?

Given the schema fully documents all parameters and an output schema exists, the description covers the essential human-level context: what the tool does, its merge behavior, the instance selection prerequisite, and the return value. It falls slightly short only in not explicitly relating to sibling tools, though that is more a usage-guideline gap.

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%, so the baseline is 3. The description only reiterates the clerk_instance_id guidance already present in the schema ('from clerk.get_connected_accounts; omit to use default') and adds no new parameter-level meaning beyond what the property descriptions already provide.

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 clearly states a specific verb ('Merge') and resource ('metadata fields for a Clerk user'), and explicitly notes that only the provided keys are updated, distinguishing it from the sibling replace_user_metadata. This makes the tool's purpose immediate and unambiguous.

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 gives clear usage context by instructing to call clerk.get_connected_accounts first and explaining how to use clerk_instance_id versus the default account. However, it does not explicitly name alternatives like clerk.replace_user_metadata or clerk.update_user, nor does it spell out when to choose this tool over them.

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