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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true, destructiveHint=false), but the description adds real value beyond them: the probe flag triggers an actual outbound request to a third-party provider, credentials are transient and never stored or echoed, and the tool is gated behind trial/Pro. No contradiction with openWorldHint.

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?

Four dense, front-loaded sentences with no filler; the core action and mode-conditional parameters come first, followed by probe semantics, return/credential notes, and the entitlement constraint. Slightly compressed but every sentence carries information.

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 11 parameters and no output schema, the description compensates by naming the return ('validation or probe status'), the credential lifecycle, and the tier requirement, while the schema covers per-field detail. It omits behavior for the custom-REST field-mapping params (promptField, systemField, responseTextPath), but those are adequately documented in the schema.

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 all 11 parameters are already documented. The description reiterates the baseUrl-vs-endpoint split by adapterMode and the probe semantics, which the schema itself states, and adds little syntax or format detail beyond that. Baseline 3 is appropriate when the schema carries the load.

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: 'Validate the HTTPS URL and adapter configuration for an external custom model.' It also delimits scope against the sibling run_custom_model by declaring 'does not perform a user prompt Send,' so an agent can separate validation from execution without opening either 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?

Gives explicit conditional guidance: use baseUrl for OpenAI-compatible mode and endpoint for custom REST, and set probe=true only when an actual external request is intended. It also states the trial/Pro prerequisite. It stops short of naming the alternative tool (run_custom_model) or stating when NOT to validate, which keeps it below a 5.

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