derive_route_shard

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 new behavioral context: the derivation is deterministic and action-independent with no network or registry access, plus a SPEC section reference. It largely reinforces rather than extends the annotation set, keeping it below 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?

Three tight sentences, front-loaded with the purpose and the exact formula, then the determinism/offline guarantees. Every clause carries information; nothing is filler.

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?

For a single-parameter pure-computation tool with an output schema and full annotation coverage, the description supplies the algorithm, the output encoding (16 bytes, lowercase hex) and the determinism guarantees. Nothing needed to invoke it correctly 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?

Schema coverage is 0%, so the description carries the burden for the single 'authority' parameter, and it does so meaningfully: 'SHA-256 of the exact authority string' signals that the raw string is hashed without normalization or trimming. It stops short of specifying encoding, whitespace or case handling explicitly.

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 (derive) and resource (ROUTE_SHARD / intent shard for an authority) and pins down the exact algorithm: SHA-256 of the authority, first 16 bytes, lowercase hex. This precision makes it clearly distinguishable from the envelope-processing siblings, and 'no lookup, no registry' rules out the lookup-style tools.

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?

It implies when the tool applies (deterministic, offline, action-independent, per SPEC sec. 3) but never names an alternative or states an explicit when-not-to-use condition. The 'no lookup, no registry, no network call' line hints at what it is not, which is useful but not framed as routing guidance.

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