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

Annotations already declare non-read-only, non-destructive, non-idempotent, so the description's contribution is the auth requirement ('Requires a full_access API key') and the null-removes-the-cap rule for daily_limit, both genuinely useful. It stops short of saying what happens on a missing ref or whether unspecified fields are left untouched, so not a 5.

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 lines: purpose first, then the changed fields, then the auth and endpoint constraints. No filler and nothing buried.

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 four-parameter mutation with no output schema, the definition supplies the permission requirement and the null-removal rule, which are the non-obvious behaviors. It omits error behavior (unknown ref, external_id collision) and partial-update confirmation, which keeps it just short of complete.

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 50% (ref and daily_limit are documented in-schema), so the baseline is 3. The description restates the null semantics already present in the schema and names the three writable fields, but adds no format, validation, or behavior detail for the undocumented name and external_id parameters.

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?

Specific verb plus resource ('Update a tenant') immediately followed by the exact set of mutable fields (name, external_id, daily_limit). The tenant resource is unambiguous against siblings like update_contact, update_domain, and update_webhook, and the endpoint/operationId removes any doubt about which underlying operation is called.

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 enumeration of mutable fields implies a partial update, but the description never says so explicitly, nor does it route the agent away from related siblings such as create_tenant, pause_tenant/unpause_tenant, or delete_tenant. Usage is inferable rather than stated.

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