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

With no annotations, the description must carry behavioral disclosure. "Show" implies a non-mutating read and the description reveals the response covers credits and plan, but it says nothing about authentication/account scoping, rate limits, or whether the balance is currency-denominated or credit-denominated.

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?

A single eight-word sentence with the primary resource (credits) front-loaded and zero filler. Nothing is padded and nothing essential is buried.

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?

For a trivial zero-param read with no output schema, the description covers the essentials of what comes back, but leaves the return shape (units, currency, plan format) undefined since no output schema exists to compensate. Adequate but with a visible gap.

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?

The tool takes zero parameters and the schema is an empty object, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly avoids inventing parameters that do not exist.

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?

"Show the account's remaining credits and plan" pairs a specific verb with two concrete resources (credits balance, plan), which is far more informative than the bare name get_balance. It does not explicitly differentiate from siblings, but the enrich_*/search_people/get_lookup set has no overlap, so misselection risk is low.

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 only implied: the description says what is returned but never states when to call it (e.g., before a paid operation to check quota) or any exclusions. For a zero-parameter read tool the implied usage is fairly unambiguous, but no explicit guidance is given.

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