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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), and the description adds value by disclosing the exact payload an agent will receive — subject, HTML, plain text, or SMS text — which no output schema provides. It does not cover failure behavior for an invalid or wrong-type template id.

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 tightly written sentences, front-loading what is fetched and what comes back, with the update-vs-fetch routing hint placed second. No filler.

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 one-parameter read tool with rich annotations, the description covers purpose, returned content and the editing alternative. Output schema is absent but the return fields are described; only error/not-found behavior is unaddressed, a minor 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% and the single parameter is documented in-schema as a template id along with its provenance (from a Spur list/search tool). The description contributes nothing further about the parameter, so the baseline 3 applies.

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 (fetch) and resource (email/SMS template) and enumerates the returned fields (subject, HTML, plain text, SMS text), which tells an agent precisely what this yields. It does not explicitly name how it differs from spur_list_message_templates or spur_preview_message_template, so sibling differentiation is implied rather than stated.

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?

Gives clear intent ('for reading or editing') and an explicit routing rule: for small changes use the update tool's replacements rather than resending the whole template. It stops short of saying when to use list or preview instead, so one usage branch is left to inference.

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