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

Annotations already declare readOnlyHint and destructiveHint=false, so safety is covered; the description adds genuinely new behavior beyond them — the response contains the full context, options, decision and reasons, and it returns null when no such decision is visible to the caller, which tells the agent how to interpret an empty result.

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 tight sentences: the core action and its scope come first, followed by the read-only and null-return facts. No redundancy or 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 one-parameter read tool with no output schema, the description covers the essential shape of the return value and the null case, which is what an agent needs. The only gap is the unexplained dual type of decision_id and no hint of where ids originate.

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?

The single decision_id parameter has 0% schema description coverage, so the description carries the burden; 'by id' and 'decision-journal entry' give minimal semantic anchoring, but nothing explains the integer-or-string union type or where such an id comes from. Adequate but thin for the coverage gap.

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 ('Read a single decision-journal entry by id') and immediately scopes it against the list form ('not just list metadata'), so the agent can distinguish it from decision_cards_list without opening a 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?

The phrase 'not just list metadata' signals the choice between this and the listing tools, and the read-only framing clarifies the operation class. It stops short of naming an alternative tool or stating explicit when-not-to-use conditions, so guidance is clear but not fully prescriptive.

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