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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false, so the mutation profile is covered. The description adds that the tool returns the new short link and that expiry makes the link stop working, but says nothing about conflict handling for a taken slug, duplicate-URL behavior, or account scoping beyond the phrase 'in the account'.

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 short sentences, purpose front-loaded with the return value, followed by the optional modifiers. Nothing is wasted and nothing essential is 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 simple 3-parameter creation tool with full schema coverage, annotations, and no output schema, the description covers purpose, the returned value, and the optional fields. Only collision/error behavior is missing, which is a minor gap rather than a blocker.

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 schema already documents url, slug format/availability, and expires_at semantics. The description's 'readable slug or an expiry date' merely restates what the schema provides, which justifies the baseline 3 rather than credit for added meaning.

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 states a specific verb and resource ('Shorten a URL in the account and return the new short link') and even names the return value. Against read-only siblings such as get_link, list_links, and get_link_stats, the creation intent is unmistakable.

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 only implied by the name; there is no explicit statement of when to call this instead of, say, list_links to check for an existing link, and no prerequisites such as account auth or slug-availability checks. The optional slug/expiry sentence hints at parameterized behavior but is not when-to-use guidance.

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