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

Annotations already declare the safe-read profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description's main added value is the auth requirement ('Needs project Read') and the full return contract. Because there is no output schema, describing what the explain actually yields (phase vocabulary, retry determination, per-data-point searchability) is genuinely load-bearing. It does not address rate limits or failure modes of the call itself.

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?

Every clause earns its place — the long first sentence is a justified enumeration of outputs that would otherwise need an output schema, and the trailing sentences handle routing and auth. It is somewhat dense and the 'Start here' cue is buried mid-paragraph rather than front-loaded, which slightly weakens scannability.

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?

With no output schema and no required parameters, the description fully compensates: it defines the return contract, the two identification paths, the auth requirement, and the entry-point condition. An agent has everything needed to select and call it correctly.

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 baseline is 3. The description's 'by its id (the ingest answer's ingestionId) or by the request id that carried it' restates the alternation the schema already documents ('when the ingestion id is not known') and adds no retrieval syntax or precedence rule beyond it.

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 names a specific verb ('explain') and resource ('one ingestion'), then enumerates the exact diagnostic content returned: phase, stop reason, retry viability, per-data-point searchability, memory counts, and next step. This clearly separates it from siblings like retry_ingestion, estimate_ingestion, and get_request, which an agent can distinguish without opening any 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?

'Start here when data does not show up' is an explicit triggering condition, and the retry-viability output implicitly routes the agent toward retry_ingestion. It also states the prerequisite ('Needs project Read') and the two ways to identify the target. It stops short of naming a sibling alternative or an explicit 'do not use this when' case, so it is strong but not exhaustive.

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