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

Annotations already establish readOnly=true, destructive=false, openWorld=false, so safety is covered. The description adds genuinely useful context beyond that: this is a legacy/deprecation status, the return is optional, and the claim must be 'owned'. It does not add detail on error cases or how the optionality surfaces, keeping it from 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?

Two sentences, front-loaded with the key discriminator ('Legacy compatibility') and a clear redirect to the modern alternative. Minimal waste, but the trailing clause about signing with sign_snack is slightly tangled relative to the otherwise sharp opening.

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-value explanation is unnecessary, and both parameters are fully documented in the schema. The description supplies the legacy/ownership context an agent needs; only minor behavioral edges (auth failure modes, what an absent payload means) are unaddressed.

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%, with claim_id and agent_token fully documented in the schema itself, so the baseline is 3. The description's reference to an 'owned historical ROOT claim' loosely maps to claim_id but adds no syntax, defaults, or interaction detail beyond what the schema already provides.

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: return Ed25519 signing bytes for an owned historical ROOT claim. It scopes the tool to the legacy/historical case and implicitly separates it from the modern path siblings (get_snack_signing_payload / sign_snack), so an agent can tell it apart 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?

Explicitly frames usage as 'Legacy compatibility' and states that new arena captures use signed ledger receipts, routing the agent to sign_snack instead. It gives clear context and an alternative, though the second sentence ('sign the artifact before capture with sign_snack') is phrased ambiguously enough that the exact when-not condition requires a little inference.

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