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

readOnlyHint already declares this as a safe read. Beyond that the description adds genuinely useful context: the underlying REST endpoint (GET /calls/{id}) and, importantly, the shape of the returned call (direction, status, duration, participants, timestamps) — valuable since no output schema exists. It does not cover error behavior (e.g. unknown id), which keeps it from a 5.

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?

One sentence front-loads the verb, resource, lookup key, and returned fields, then appends the REST mapping. No filler; every clause earns its place.

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, listing the returned fields is exactly the right compensation, and the id format covers the only input. Missing is any note on failure modes or how to obtain a valid id, which would round out a single-parameter getter.

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 coverage is 100% and the single parameter is fully documented there, so the baseline is 3. The description's "starts with 'AC'" note simply repeats the schema's own id description and adds no format, uniqueness, or lookup guidance beyond it.

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 ("Get a single call by its id") and enumerates the fields the call object contains, which implicitly distinguishes it from list_calls and the get_call_recordings/summary/transcript sub-resource siblings. It stops short of naming an alternative explicitly, so it is clear but not fully sibling-differentiating.

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 id-prefix condition ("starts with 'AC'") and the by-id framing imply when this tool is appropriate, but there is no explicit when-to-use/when-not guidance and no pointer to list_calls for discovery or to the sub-resource getters for recordings/transcript/summary.

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