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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is partly covered. The description still adds real value by enumerating exactly which side effects do NOT occur (no charge, no job, no reservation), which directly addresses an agent's fear about calling a cost tool. It omits return shape and any rate/permission notes.

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 short sentences, front-loaded with the core meaning and free of padding. The three negation clauses are mildly redundant in tone but each targets a distinct concern, so the text still earns its length.

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 low parameter coverage, the description should carry more. It adequately implies the return value (a credit figure) and rules out side effects, but leaves the key required 'operation' parameter and 'units' undefined, so an agent cannot fully construct a correct call from the definition alone.

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 only 33%: url is documented, but 'operation' (the sole required parameter) and 'units' are not, and there is no enum to constrain operation. The description says cost is 'per operation' but never explains what values operation accepts or what units means, so it fails to compensate for the coverage gap.

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 states a specific outcome: the credit cost an operation would incur for this account. It is clearly distinguishable from get_credits (balance) and crawl_site (action), but it never names a sibling to route the agent, so it stops short of a 5.

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?

Usage is implied rather than stated: the three negative clauses ('Never charges', 'Never creates a job', 'Does NOT reserve credits') make clear this is a safe dry-run pre-check. There is no explicit when-to-use or when-not-to-use guidance and no mention of how it relates to get_credits or the tools whose costs it estimates.

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