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

Annotations already declare read-only, open-world, non-destructive; the description adds substantive context beyond them: no credentials or query parameters, sideboards and Moxfield companions excluded, no private access, and no saved server copy. It also discloses the return shape (quantity-prefixed main-deck text, tagged commander, card count, warnings), which no output schema provides.

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 action and source, followed by scope, exclusions, and recovery. Every sentence carries information, but the density makes it read as a run-on list and the *CMDR* fallback instruction sits awkwardly at the end.

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?

Covers input format, output shape, exclusions, error handling, and the recommended next step — everything an agent needs to call this correctly. The only minor omission is that idempotentHint=false (repeated fetches may see changed decks) goes unmentioned, but nothing critical 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?

With one parameter at 0% schema coverage, the description carries the burden and does so well: it specifies the URL must be public HTTPS, from Moxfield or Archidekt, and free of query parameters. It does not mention the 500-character limit or URL syntax edge cases, so it falls short of full compensation.

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 ('Read a public HTTPS Moxfield or Archidekt deck URL') and names the supported sources. It is unmistakable against siblings like build_mana_base or repair_deck, which transform decks rather than ingest them from a URL.

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?

Explicitly routes the agent forward ('Follow with a deck-review tool to validate names and legality') and handles the failure case ('If Moxfield access is blocked, do not repeat the URL request'), including a concrete fallback of asking the user for Download > Copy Plain Text with *CMDR* marking. This is when/when-not guidance with alternatives, not implicit usage.

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