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

Annotations already declare readOnly, non-destructive, non-open-world, and non-idempotent behavior, so the safety profile is covered. The description goes beyond that by enumerating what each mode returns (resource keys, meanings, record counts, parent relationships, sync times, filterable/orderable/summable columns), which is genuinely additive.

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?

Purpose is front-loaded, but the two sentences are dense run-ons ('how many records it holds and what it hangs off', 'the columns search_records filters and orders by and summarize_records sums and groups by') that are hard to parse. The mode-based colon structure helps, but the prose is longer than it needs to be.

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 zero required parameters, the description correctly carries the return-value burden and specifies the content of both call modes. What's returned is well covered; only the practical trigger for using this versus sibling introspection tools is thinly addressed.

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 earns above baseline by explaining the functional difference the `resource` parameter makes — omitting it yields the full inventory, including it enriches output with sync times and column semantics — adding meaning beyond the schema's terse 'a resource key, or several'.

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 opens with the noun phrase 'What a source's backup holds' rather than a clear verb+resource statement, so the tool's action is left implicit. It does convey that the tool reports on resources/records, but the oblique framing ('what it hangs off') is vaguer than a clean 'Describe the resource keys in a source'.

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 distinguishes two modes ('Without resource: ...' vs 'Name one resource or several to add ...'), which is useful contextual guidance. However it never states when to pick this tool over siblings like discover_operations or get_started; the references to search_records/summarize_records are relational, not alternative-routing guidance.

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