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

Annotations already declare the mutation/idempotency/safety profile (readOnly=false, idempotent=true, destructive=false), and the description correctly aligns with them. It adds genuinely useful non-annotation constraints: JPEG or PNG only, 5MB cap, and that content_type pairs with data. It omits any note about permissions or what happens to the prior photo.

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, with the core action and the mutual-exclusion rule front-loaded ahead of the format/size limits.

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 mutation with no output schema, the description covers the input contract and validation limits well. It does not mention the two required identifiers (profile_id, phone_number_id) that scope the operation, which is the only notable 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?

Schema coverage is 100%, so the baseline is 3, but the description adds a cross-parameter constraint the flat schema does not express: url and data are mutually exclusive alternatives, and content_type is required only when using data. That is meaning beyond the field-level descriptions.

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 ('Replace the profile photo of a phone number'), which is clearly distinct from the sibling whatsapp_business_profile_update that edits other profile fields. An agent can select this without opening the 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 description gives clear in-tool guidance on the exclusive url-vs-data choice, but never says when to use this tool rather than whatsapp_business_profile_update or when removal/replacement is appropriate. Usage is implied rather than framed against alternatives.

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