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

Annotations already show this is mutating but not destructive. The description adds the partial-update behavior ('send only the fields to change'), which is useful context. It doesn't discuss response, side effects, or permissions, but with annotations covering the safety profile this is acceptable.

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 concise sentences with no filler. The action is front-loaded and the key usage instruction follows immediately.

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 simple partial-update tool with a fully documented schema and clear annotations, the description is adequate. It covers the operation type and the update pattern; the required endpoint_id is visible in the schema, and there is no output schema to describe.

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 description coverage is 100%, so the baseline is 3. The description adds the patch semantics and references create_api_endpoint for the field set, but doesn't need to restate individual parameter meanings since the schema already documents them.

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 action ('Patch an existing custom API endpoint') with a clear verb and resource. It distinguishes itself from create_api_endpoint by saying 'existing' and referencing the same field set, so an agent can tell update from create without opening schemas.

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?

Gives an explicit usage rule: send only the fields to change. It also points to create_api_endpoint as the reference for the field set, establishing an update-vs-create context. It doesn't explicitly name alternatives like set_endpoint_auth, but the main use case is clear.

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