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

With no annotations at all, the description carries the full behavioral burden and does so well: it discloses that changing the address preserves the old redirect, that old-address clicks still count on the link via `previousShortUrls`, that placements follow the domain change, and that archiving stops redirection (old addresses included) while retaining history. These are non-obvious side effects an agent genuinely needs.

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 tight sentences: the mutating scope is front-loaded, then the redirect-preservation behavior, then the archive/never-delete semantics. No filler, and the most decision-relevant facts come first.

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 six-parameter mutation tool with no annotations and no output schema, the description covers the important behavioral consequences well. It stops short of stating permission requirements or whether omitted fields are left unchanged, which leaves a small gap for a mutation tool.

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 every parameter is already documented in the schema, including `slug_taken` errors and the shared-domain value. The description adds little parameter-level meaning beyond confirming which fields are updatable, so the baseline 3 applies.

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 verb and resource (modify a link) and enumerates exactly which fields can change: destination, label, address (domain/slug), archive. It is clearly distinct from create_link/get_link/list_links by virtue of the `id`-based mutation, though no sibling is named explicitly, which keeps it short of a 5.

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?

Usage is implied (call it to alter an existing link identified by `id`) but there is no explicit when-to-use statement, no guidance on partial vs full updates, and no exclusions or named alternatives. The reader must infer the context from the verb alone.

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