Verify credentials and upstream reachability

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

Annotations already declare readOnly/idempotent/openWorld, so the safety profile is covered. The description still adds real value beyond them: the guarantee that the credential itself is never returned, and a taxonomy of failure modes ('no credential' vs 'credential rejected' vs upstream problem) plus the steps/failed_step breakdown. Some of that last detail is return-shape information an output schema would normally carry.

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 and the ordering of the probe are front-loaded, and the when-to-use clause lands at the end. It is dense but slightly long, with the em-dash clause packing return details that could be tighter.

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, the description must carry the return contract, and it does: credential source, acceptance, round-trip time, a plain-English hint, and the steps/failed_step fields. Nothing an agent needs to interpret the result correctly is missing.

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?

Zero-parameter tool, so the baseline is 4. The description correctly implies no inputs are needed to run the probe and describes only the outputs it produces.

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 sequence and resource: resolve the credential the way real tools do, then make one authenticated request to creditkarma.com. This clearly distinguishes it from the read/data siblings (ck_list_transactions, ck_get_account_summary) as a diagnostic probe rather than a data fetch.

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?

Explicit trigger given: 'Call this when a real tool fails and you want to know which hop broke.' It also names the failure-localization mechanism (steps, failed_step) that selects this tool over simply retrying a sibling.

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