validate_completion_metadata

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

The non-mutating claim ('without making changes') largely restates the existing readOnlyHint/destructiveHint=false annotations, so it earns limited extra credit. The description does add useful context about the cost of skipping validation, but it says nothing about failure behavior — whether it returns all errors at once, throws, or returns a partial report. With annotations covering the safety profile and an output schema present, a 3 is appropriate.

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 short sentences, both front-loaded with the action and its timing. No filler, no restated name, and the 'why' arrives after the 'what'.

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?

Given an output schema, rich annotations and full parameter documentation, the description covers what the tool does and when to reach for it. The only meaningful omission is what a validation failure looks like and whether optional attribution fields are checked at all.

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 baseline would be 3, but the description adds a real semantic hint: the tool checks *required* fields, which is notable because the schema declares no required array (requiredness lives only inside individual parameter descriptions for app and env). It still doesn't name which parameters are mandatory or how optional ones like client_id/project_id are treated.

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 (validates) and resource (billing metadata), plus a named scope ('preflight ... before run_prompt_completion') that distinguishes it from the actual completion-calling sibling. An agent can tell exactly what it does and where it sits in a sequence.

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 prescribes the ordering: call this before run_prompt_completion. It also gives the motivation ('catch attribution errors before paying for the call'), which tells the agent the cost consequence of skipping it. Rival tools that consume metadata are implicitly excluded.

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