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

Annotations already carry readOnlyHint=false, idempotentHint=true, and destructiveHint=true, so the bar is lower. The description adds valuable context beyond the hints: it specifies the write destination ('record the receipt in the open ledger') and elaborates the idempotency ('Replaying the same signature is idempotent'), telling the agent a repeat call is harmless. It does not explain what the destructiveHint=true actually destroys (e.g., overwriting a prior receipt), a minor gap, but there is no contradiction with any annotation.

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 sentences with zero filler. The action, scope, and destination are front-loaded in the first sentence, and the idempotency guarantee is a tight second sentence. Every clause earns its place; nothing is redundant with the schema.

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?

An output schema exists, so return values need no explanation. Schema coverage covers parameters, and annotations cover safety/idempotency. The description covers the key operational facts (owned scope, ledger write, idempotent replay). The only omission is elaboration of the destructive semantics beyond what the hints flag, a minor shortfall for a medium-complexity write tool.

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 itself already documents all four parameters (key_id, snack_id, signature, agent_token) with patterns and provenance references. The description loosely aligns with parameters (Ed25519 signature, owned snack) but does not add meaning beyond the schema. Baseline 3 is correct given full schema coverage.

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+resource+scope: 'Attach an optional Ed25519 author signature to an owned snack and record the receipt in the open ledger.' The 'owned snack', 'optional', and 'Ed25519' qualifiers plus the ledger-recording outcome sharply distinguish it from siblings like sign_root_takeover and get_snack_signing_payload. An agent can tell what this does and how it differs without opening other schemas.

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 description implies usage context — it applies to 'an owned snack' and the signature is 'optional' — which signals when an agent might choose this tool (when the user wants authorship recorded). However, it names no alternatives and gives no when-not-to-use guidance; the agent must infer the routing vs. siblings like sign_root_takeover. That is adequate but not explicit.

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