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

Annotations already declare a non-read-only, non-idempotent, non-destructive mutation with a closed-world scope, and the description adds genuinely useful negative guarantees: no carrier settings change, no number purchase, no phone call. It omits important behavior for a mutation tool, such as the optimistic-concurrency role of base_revision and what happens to unspecified fields.

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 sentences, front-loaded with the scope and immediately followed by the most important negative guarantees. No filler, though the middle sentence could be folded in without loss.

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 an 11-parameter, five-step mutation tool with no output schema and only generic annotations, the description leaves the workflow semantics largely unexplained—the agent cannot tell what 'step' selects or how base_revision must be supplied. What is present is accurate but insufficient.

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 only 27%, yet the description explains almost nothing about the 11 parameters—the meaning of the 'step' enum values, base_revision, line_type, number_id, provider_key, and agent_id are all left undocumented. It touches source_number ('existing-number') and the test step's evidence precondition, but this is far from compensating for the coverage gap.

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 names the resource (an existing-number forwarding setup) and the constraint that only existing setups are touched, which distinguishes it implicitly from create_forwarding_setup. However, the operative verb is the vague 'Manage' rather than 'update', and no sibling is named directly.

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?

There is no explicit guidance on when to call this versus create_forwarding_setup, get_forwarding_setup, start_forwarding_test, or cancel_forwarding_test—all of which appear in the sibling list. The phrase 'existing-number forwarding setup' hints that creation is excluded, but the agent must infer that.

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