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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the description need not repeat those. It adds the Pro-plan restriction for setting an expiry and clarifies that the short code remains unchanged, which is useful. However, it does not disclose the mutual exclusivity of expires_in_days and remove_expiration (though the schema states it) or any error conditions, so it adds moderate value beyond annotations.

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 sentences with no filler. The primary action is front-loaded, and the constraint on the short code is stated at the end. Every word earns its place, making it efficient and well-structured.

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 4-parameter tool with full schema coverage and annotations covering safety, the description is adequate but not fully complete. It omits the mutual exclusivity of the expiry parameters (though the schema states it), any return-value expectations (no output schema exists), and prerequisites like the link needing to exist. It covers the core operations but leaves some contextual gaps.

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 each parameter already has a description. The description adds a high-level mapping: 'Change where a link points' to url, 'set a new expiry' to expires_in_days, 'remove its expiry' to remove_expiration, and 'short code stays the same' to code. It also reveals the Pro requirement for expiry, which is not present in the schema, providing meaning beyond what the schema alone offers.

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 the action ('Change where a link points') and the resource (link), and specifies what can change: destination URL and expiry (set or remove). It distinguishes from siblings like delete_link and create_link by focusing on modification, and the note 'short code stays the same' further scopes the operation.

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 implies usage when modifying an existing link, but it does not explicitly contrast with alternatives like create_link or delete_link, nor does it mention prerequisites (e.g., the link must exist). There are no exclusions or when-not-to-use guidance, but the context is clear enough that an agent can infer it's for updates.

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