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

Annotations already declare readOnlyHint/idempotentHint, so the safety profile is covered, but the description adds real behavioral context: append-only ledger, an immutable snapshot that is never recomputed, and a typed DECISION_NOT_FOUND refusal for unknown ids. It also flags that no payment is required, which matters on a paid platform. It does not discuss rate limits or auth, hence 4 rather than 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?

Front-loads 'FREE read' and the lookup key, then enumerates the returned fields, error behavior and cost in compact clauses. Minor redundancy between the leading 'FREE' and the trailing 'No payment required', which is the only thing keeping it from a 5.

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-param read with an output schema, the description supplies everything the schema and annotations cannot: the immutability guarantee, the shape of the record (probability, confidence, policy verdict, hashes, payment linkage), the typed error for missing ids, and the zero-cost property.

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?

There is only one parameter, and the schema itself fully constrains it (string, uuid format, explicit pattern). The description restates 'by decision_id (UUID)' without adding semantics the schema lacks, so this is baseline adequacy.

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 gives a specific verb (read) plus resource (a past decision from the append-only ledger) and the lookup key (decision_id UUID), and it implicitly separates itself from tollbridge_decision by stressing 'past' and 'never a recomputation'. It stops short of naming the sibling tools (e.g. tollbridge_decision, tollbridge_get_resolution) explicitly, so differentiation requires a small inference.

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?

Usage is implied: use this when you already hold a decision_id and want the recorded decision rather than a fresh computation. There is no explicit when-not guidance and no named alternative tool, so an agent must infer that recomputation lives elsewhere.

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