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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that: it is a pure identifier translation ('Does not fetch the profile') and produces a 17-digit SteamID64, which is the closest thing to a return contract given there is no output schema. It doesn't say what happens for unknown vanity names or private profiles, which keeps it off a 5.

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?

Front-loaded with the core action and efficient overall, but the third sentence largely re-says the opening line ('Turn a ... link, or a custom URL name, into the SteamID64') rather than adding new information. Slight redundancy costs it a point.

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?

With one parameter and no output schema, the description supplies the missing return semantics (a 17-digit SteamID64) and the critical negative behavior (does not fetch the profile). What's absent is failure behavior for invalid or unresolvable identifiers, which an agent would benefit from knowing before calling.

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 single `q` parameter already documents the accepted forms (profile URL, custom URL name, SteamID64). The description's URL examples are essentially a restatement of the schema rather than added meaning — no format normalization rules or precedence between accepted forms are given. Baseline 3 is correct.

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+resource ('Resolve a profile URL or vanity name to a SteamID64') and explicitly distinguishes itself from profile-fetching tools with 'Does not fetch the profile.' An agent can place it against siblings like get_player_stats, get_inventory, and get_server without opening a 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?

The final sentence names the downstream consumers ('the SteamID64 the inventory and player tools need'), which gives clear context for when to reach for this tool. It stops short of naming an alternative or an explicit when-not-to-use case, but for a single-purpose resolver the routing signal is clear.

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