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

Beyond the provided annotations (readOnlyHint=false, idempotentHint=true), the description discloses two high-value traits: changes propagate within 30s without redeploy, and an immutable-parameter violation is atomic ('rejects the whole call, with nothing applied'). That is exactly the operational context an agent cannot infer from the annotation set.

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?

Two sentences, no filler. The mutation scope and effect are front-loaded, with the failure-mode caveat second, which is the right ordering for a caller deciding whether to invoke.

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 14-parameter mutation tool with no output schema, the description covers scope, immutability, atomicity and propagation latency well. The one notable omission is whether omitted fields are left unchanged (partial update) or cleared, which matters for a bulk-metadata updater.

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 36%, so the description carries real weight: it names all eight mutable parameters and confirms which four are immutable, aligning with the schema's IMMUTABLE markers. It does not clarify semantics such as patch-vs-replace or timeout_ms units, leaving a modest 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?

States a specific verb ('Update') plus resource ('a Function's mutable metadata') and enumerates exactly which fields are mutable, so an agent can distinguish it from create_function, delete_function and the sibling update_* tools without opening any 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?

The mutable/immutable split functions as a clear when-to-use/when-not guide: it warns that entity_id, name, trigger_point and language will reject the entire call. It does not name alternative tools explicitly, so it stops just short of the top band.

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