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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered and the output schema defines the return shape. The description adds only the scoping detail that the balance is for the connected account; it says nothing about freshness, currency units, or what a zero/exhausted balance looks like.

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 front-loaded sentence with no filler, hedging, or redundant restatement of the title. Every word carries meaning.

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 parameters, an output schema covering return values, and annotations covering safety, a one-sentence description is close to sufficient. The only minor gap is that it does not clarify whether the balance is a live figure or a cached snapshot.

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?

There are zero input parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The schema is empty and fully consistent with the description.

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 uses a specific verb and resource ('Returns the credit balance') and scopes it to 'the connected account', which cleanly separates it from mutable siblings like set_spend_limit and from the forward-looking estimate_cost. It stops short of explicitly naming those siblings, so it is clear but not fully differentiated.

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?

The zero-parameter, read-only nature makes the usage largely self-evident, but the description never states when to call this versus estimate_cost (projected spend) or set_spend_limit (managing the limit), and gives no exclusions or preconditions.

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