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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description meaningfully adds 'credential-free public Letterboxd data', telling the agent no auth is needed, which is genuine context beyond the structured fields. It adds little about return behavior, but an output schema exists to carry that.

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?

The purpose is correctly front-loaded in the first sentence. However, the limit and slug sentences duplicate schema descriptions that are already at 100% coverage, so those clauses do not earn their place and add noise.

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 two-parameter lookup with an output schema and safe read annotations, the description covers purpose, auth posture, and how to obtain the slug. It is close to complete; only explicit routing against sibling film tools is missing.

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%, and the description merely restates both parameter descriptions verbatim ('limit: Max films, default 10, max 50', 'slug: Letterboxd film slug, e.g. parasite-2019'). It adds no syntax or constraint detail beyond the schema, 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?

The description gives a specific verb and resource: returns films Letterboxd recommends as similar to a given film. This is clearly distinguishable from letterboxd_film (details) or letterboxd_search, though it never explicitly names a sibling for contrast. An agent can tell what it does without opening the schema.

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?

It points to letterboxd_search for finding a film, but that is a prerequisite for the slug rather than a true when-to-use / when-not-to-use rule. There is no explicit statement of when to prefer this tool over letterboxd_film or other related siblings, so guidance is only implied.

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