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

Annotations already declare the write/idempotent/non-destructive profile, and the description goes well beyond them: earliest valid ballot wins, duplicates are logged rejected, no vote-changing, auth is the operator's Ed25519 signature verified service-side, and no x402 payment challenge is added by the MCP layer. These are exactly the failure-mode and cost facts an agent needs before calling a write.

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 critical facts are front-loaded, but the no-payment point is restated three times ('FREE — no payment required', 'no x402 challenge; this tool is free', 'the MCP layer adds no payment to it'), which is redundant weight in an otherwise dense paragraph.

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 auth mechanism, duplicate handling, cost, and the raw HTTP equivalent — substantial for a write tool with no output schema. The remaining gap is that it never says what a successful cast returns (receipt, tally acknowledgement) nor resolves the id/proposal_id duality.

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 20%, so the description must compensate, and it does explain the `signature` canonical string format. However it never disambiguates `id` vs `proposal_id` (the canonical string uses {proposal_id} while the required field is `id`), leaving the most consequential ambiguity unresolved.

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 ('Cast ONE ballot') and immediately bounds the scope with '(operator-key-signed write; agents never vote)'. An agent can distinguish this from commons_get_vote_status or commons_create_proposal without opening any 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?

Gives a strong eligibility rule ('agents never vote'), a one-ballot-per-operator rule, and states that vote changes are impossible, which tells the agent when this call is pointless. It does not name a sibling for the read-side check (e.g. commons_get_vote_status), so it stops short of full alternative routing.

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