Substack MCP Server

Server Quality Checklist

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Latest release: v1.0.0
Disambiguation5/5
Each tool targets a distinct action or resource: drafts, notes, published posts, sections, subscribers, scheduled posts, and image upload. There is no overlap or ambiguity between the tool purposes.
Naming Consistency5/5
All tool names follow a consistent verb_noun pattern using snake_case (e.g., create_draft, get_post_analytics, list_drafts). The naming convention is uniform and predictable.
Tool Count5/5
14 tools is well-scoped for a Substack publishing server. It covers drafting, notes, posts, analytics, comments, sections, subscribers, scheduling, and image upload—each tool earns its place without redundancy.
Completeness2/5
Critical lifecycle operations are missing: no way to publish drafts, delete content (posts, notes, drafts), or schedule long-form posts. The server creates drafts and notes but leaves users unable to complete the publishing workflow within the toolset.
Average 4.2/5 across 14 of 14 tools scored. Lowest: 3.4/5.
See the Tool Scores section below for per-tool breakdowns.
- 3 of 3 community issues answered or closed in the last 6 months
- 31 commits in the last 12 weeks
- Last stable release on August 3, 2026
- No critical vulnerability alerts
- No high-severity vulnerability alerts
- No code scanning findings
- CI is passing
This repository is licensed under MIT License.
This repository includes a README.md file.
No tool usage detected in the last 30 days. Usage tracking helps demonstrate server value.
Tip: use the "Try in Browser" feature on the server page to seed initial usage.
This repository includes a glama.json configuration file.
This server has been verified by its author.
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How is the quality score calculated?

The overall quality score combines two components: Tool Definition Quality (70%) and Server Coherence (30%).

Tool Definition Quality measures how well each tool describes itself to AI agents. Every tool is scored 1–5 across six dimensions: Purpose Clarity (25%), Usage Guidelines (20%), Behavioral Transparency (20%), Parameter Semantics (15%), Conciseness & Structure (10%), and Contextual Completeness (10%). The server-level definition quality score is calculated as 60% mean TDQS + 40% minimum TDQS, so a single poorly described tool pulls the score down.

Server Coherence evaluates how well the tools work together as a set, scoring four dimensions equally: Disambiguation (can agents tell tools apart?), Naming Consistency, Tool Count Appropriateness, and Completeness (are there gaps in the tool surface?).

Tiers are derived from the overall score: A (≥3.5), B (≥3.0), C (≥2.0), D (≥1.0), F (<1.0). B and above is considered passing.

Tool Scores

Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=true, and the description aligns (a listing operation is read-only). The description adds value by noting the returned fields, which supplements what annotations provide. There is no contradiction, and it adds contextual detail about the output shape beyond the annotation's safety declaration.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single concise sentence that states purpose and output fields with zero waste. Could arguably add sibling-differentiation guidance, but as written it is efficient and front-loaded.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
No output schema exists, so the description's statement of returned fields (title, creation date, audience) is the only return-shape documentation—it's helpful but minimal. For a simple listing tool with readOnly annotation and two well-documented params, this is adequate but not rich; pagination behavior or sorting could be noted to improve completeness.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters2/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the schema documents both params (limit, offset). However, the description adds no param-related meaning beyond the schema—it doesn't mention pagination, defaults, or how limit/offset interact. Since schema coverage is high, baseline is 3, but the description contributes zero additional parameter semantics beyond what's structured, so a slight deduction is warranted.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose4/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description names a specific verb+resource ('List draft posts') and states the returned fields (title, creation date, audience). It doesn't explicitly distinguish from siblings like list_published_posts or list_scheduled_posts, but the resource name (drafts) along with the returned fields is reasonably clear.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
No explicit when-to-use or alternative guidance. However, the sibling set includes list_published_posts and list_scheduled_posts, and 'draft' in the name plus 'audience' field implies it's for unpublished drafts. Context is implied but not stated; no exclusions or alternatives are named.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior2/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true. The description adds that it returns 'title, body HTML, metadata', but no additional behavioral traits. No contradiction, but adds minimal value beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single sentence, directly states purpose and output. No wasted words. Front-loaded with action and resource.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple read tool with one parameter and known annotation (readOnlyHint), the description fully explains what is returned, making it complete for an agent to select and invoke correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and already describes post_id as 'The post ID to retrieve'. The description only repeats 'by ID', adding no new meaning. Baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'Get', the resource 'a published post by ID', and the return value 'title, body HTML, metadata'. It distinguishes from sibling tools like 'get_draft' (draft vs published) and 'list_published_posts' (list vs single).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage for retrieving a published post's full content, but does not explicitly state when to use this over alternatives like 'get_draft' or 'list_published_posts'. No exclusions or context provided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, so the description does not need to restate that. It adds value by specifying return content (title, body, metadata), but no other behavioral details like permissions or error cases.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single sentence, front-loaded with action and return values. No wasted words. Efficient and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple read-only tool with one parameter and no output schema, the description covers the essential purpose and return structure. Minor gaps include lack of error handling or metadata format, but overall adequate given the complexity.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% (draft_id described as 'The draft ID to retrieve'). The description adds no additional meaning to the parameter beyond what the schema provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description explicitly states the action ('Get the full content of a draft post by ID') and the return values ('title, body, metadata'). This clearly distinguishes it from siblings like get_post or list_drafts.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
No explicit guidance on when to use this tool versus alternatives. The description implies you need a draft ID, but does not differentiate from get_post or list_drafts.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate non-destructive modification (destructiveHint=false, readOnlyHint=false). The description adds that it accepts markdown body and only applies to unpublished drafts, which provides some behavioral context beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is extremely concise with only two sentences and no fluff. Every word serves a purpose, making it highly efficient.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
While the purpose and constraint are clear, the description does not clarify whether updates are partial or full, nor does it mention return values or error scenarios. Given the lack of an output schema, some additional context would be helpful for an AI agent.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the schema already documents all parameters and their purposes. The description mentions 'accepts markdown body', but this is also covered by the body parameter's description in the schema. No additional semantic value is added.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states 'Update an existing draft post' which accurately conveys the action and resource. The additional constraint 'Only works on unpublished drafts' further distinguishes it from siblings like get_draft or list_drafts.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implicitly guides usage by specifying that it only works on unpublished drafts, but it does not explicitly state when to use this tool over alternatives like create_draft or get_draft. Still, the constraint provides clear context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, and the description consistently aligns by listing published posts (a read operation). The description's main added value is the return field disclosure. It doesn't contradict annotations. Some behavioral detail (pagination clamping, rate limits) is in the schema rather than description, which is acceptable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single sentence, front-loaded with the action, zero filler. Every word earns its place.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple paginated list tool with readOnlyHint annotation, 100% schema coverage on both params, and no output schema, the description is adequate. It declares the return fields which compensates for the missing output schema. Could mention pagination behavior or total counts, but not critical for correct usage.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, with both limit and offset documented including the Substack clamping behavior. The description itself adds minimal parameter meaning, but the schema does the heavy lifting, so baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description uses specific verb+resource ('List published posts') and specifies the return payload shape (title, date, slug, URL). It clearly distinguishes from siblings like list_drafts and list_scheduled_posts by scoping to published posts.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies this is for browsing published posts, and the sibling list distinguishes it from drafts/scheduled posts. However, there is no explicit when-to-use guidance or alternative naming, though the tool name itself is reasonably unambiguous.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, which aligns with 'Get comments'. Description adds value by specifying exact return fields, going beyond annotations. No contradictory or missing behavioral info.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single sentence, front-loaded with verb and resource. No unnecessary words, concise and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Adequate for a simple read-only tool. Specifies return fields and limit behavior. Could mention pagination or sorting, but not essential given simplicity.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema covers 100% of parameters with descriptions. Description doesn't add input parameter details but compensates by explaining output semantics (returned fields) since output schema is missing.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Description clearly states 'Get comments on a published post' with specific return fields (commenter name, comment body, date, reaction counts). Distinguishes from sibling tools like get_post and create_draft by focusing on comments.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides clear context for use (published post) but lacks explicit guidance on when to use vs. alternatives. No exclusion criteria or sibling comparison.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The readOnlyHint annotation already signals a safe read operation, but the description goes beyond it by explaining the three precision modes ('exact', 'approximate' with the hedged rendering guidance, and 'unavailable' with count -1). This is genuinely useful behavioral context about return value semantics, not just repetition of the annotation. It could add what errors occur or rate limits, but for a read tool this is solid.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences, zero waste. Every sentence adds value: purpose and precision-mode semantics, and the critical warning not to treat approximate as exact. Front-loaded with the core purpose.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a 0-parameter read tool with no output schema, the description explains the return shape (precision modes and count values) thoroughly. It covers the edge case of 'unavailable' and the rendering guidance. Complete enough for an agent to invoke and interpret results correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 0 parameters, there's nothing for the description to clarify. The baseline of 4 applies for zero-parameter tools; the description appropriately focuses on return-value semantics instead, which is the semantically meaningful content here.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool gets the current subscriber count for a Substack publication. The verb+resource (get subscriber count) is specific and distinguishes it from siblings, which all deal with posts, drafts, sections, and analytics.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description does not explicitly state when to use this tool vs alternatives, but for a 0-parameter retrieval tool the usage context is largely self-evident. It doesn't provide when-not-to-use guidance or alternatives, but given there's no close sibling (no other subscriber-related tool), the lack of exclusions is acceptable. The precision-mode guidance is user-facing behavior rather than tool-selection guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds valuable context beyond the readOnlyHint annotation: it explicitly discloses that scheduling/publishing/deleting is NOT performed by this server, preventing the agent from assuming this tool can schedule posts. It also clarifies the read-only nature with 'Read-only visibility into what's queued.' The readOnlyHint already covers the safety profile, and the description reinforces it with concrete scoping.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three concise sentences with zero waste. Front-loaded with the primary purpose, immediately clarifies scope boundaries (what it doesn't do), and lists the return fields. Every sentence earns its place.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple read-only list tool with 100% schema coverage, full param documentation, a strong readOnlyHint annotation, and clear scope disambiguation from siblings, the description is complete. It explains what it returns, the ordering, what it does NOT do, and its relationship to the broader system.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so both parameters (limit, offset) are already fully documented in the schema with their defaults and clamping behavior. The description adds the list ordering ('soonest first') which is useful context, but doesn't add significant param semantics beyond what the schema provides. Baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Specific verb+resource: 'List posts scheduled for future publication, soonest first.' Clearly distinguishes from siblings like list_published_posts and list_drafts by focusing on scheduled/future posts. States exactly what is returned (id, title, audience, trigger_at).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explicitly notes 'scheduling itself is done in Substack's editor' and that 'this server does not schedule, publish, or delete long-form posts,' which disambiguates from create/update tools. It also clarifies this is read-only visibility into the queue. A clear alternative is implicitly established via the sibling list_published_posts, though it doesn't explicitly name the alternative tool for publishing.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate readOnlyHint=false and destructiveHint=false, meaning the tool is a write operation. The description adds behavioral context: it accepts markdown and converts it, and it does not publish. This goes beyond the annotations, providing useful details about the tool's behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is two sentences, front-loaded with the primary action, and includes both the core function and a key constraint. Every sentence adds value with no wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
The tool has 4 parameters and no output schema. The description covers the main behavior (creating a draft with markdown conversion) and the non-publishing aspect. It does not detail return values or prerequisites, but for a straightforward creation tool, the description is sufficiently complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the baseline is 3. The description adds context for the 'body' parameter by stating 'Accepts markdown body which is converted to Substack's format', which clarifies the expected input format beyond the schema's description. This extra information warrants a score of 4.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the action ('Create a new draft post'), the resource ('draft post'), and distinguishes from publishing ('Does NOT publish'). The verb 'create' and resource 'draft post' are specific, and the description differentiates from siblings like 'update_draft' or 'get_draft'.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explicitly states 'Does NOT publish — creates a draft only', which helps the agent understand when to use this tool versus a publishing tool. It provides clear context but does not explicitly mention when not to use it or name specific alternatives beyond the implication.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior5/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond annotations (readOnlyHint=false, destructiveHint=false), the description adds critical behavioral details: immediate publication, no draft state, irreversible action due to lack of delete tools. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences with no waste: purpose, input format, and critical caveat. Information is front-loaded and each sentence earns its place.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple tool with one parameter and no output schema, the description covers purpose, input, and behavioral traits. Could mention return value (e.g., created note object), but overall sufficient.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and the description only restates 'markdown text' already present in the schema. No additional semantic value beyond what the schema provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states it creates a Substack Note (short-form content) and accepts markdown text, distinguishing it from sibling tools like create_draft (long-form) and create_note_with_link (note with a link).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
It explicitly warns that notes publish immediately with no draft state and no undo, implying when to use (for instant public notes) and when not (if drafts or reversibility are needed). Could be more explicit about alternatives, but the context with siblings helps.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior5/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds critical behavior not in annotations: immediate publication, no draft state, no undo. This matches the annotations (readOnlyHint=false, destructiveHint=false) and provides full transparency.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, front-loaded with purpose, then caveats. No wasted words. Efficient and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple tool with two parameters and no output schema, the description covers purpose, behavior, and caveats. It references create_note for additional context. Could mention error handling or response format, but not essential for basic understanding.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with good descriptions. The tool description adds the detail that the URL is displayed as a rich card, but this is already in the schema. No substantial additional meaning is provided.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool creates a Substack Note with a link attachment displayed as a rich card. It distinguishes from sibling tools by explicitly mentioning the link card and referencing 'create_note' for plain notes.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description mentions 'same caveats as create_note: no draft state, no undo', which guides when to use it versus creating drafts. However, it does not explicitly mention that for plain notes one should use 'create_note', though this is implied by the context of sibling tools.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotation already declares readOnlyHint=true, and the description adds that it returns id and name, which is consistent and sufficient. No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two concise sentences: first states purpose and output, second gives usage guidance. No unnecessary words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple list tool with no parameters and no output schema, the description fully covers what the tool does, returns, and how to use it.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
No parameters exist, so schema coverage is 100%. The description does not need to add parameter explanations, meeting the baseline for 0 parameters.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'list' and the resource 'sections', and it distinguishes itself from sibling tools by focusing on listing categories.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
It provides explicit guidance on using the section ID for drafts, which is the primary use case. However, it does not mention when not to use it, but that is acceptable for a simple list tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior5/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds critical behavioral context beyond the readOnlyHint annotation: the tool searches a limited set of recent posts and returns a not-found note if absent. This fully discloses the workaround behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences with no filler. The first sentence lists all returned stats, the second explains the internal search limitation. Every word is useful and front-loaded.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a single-parameter tool with no output schema, the description fully covers what to expect (list of stats fields), the search limitation, and the not-found behavior. It is sufficient for an agent to decide when to call.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema covers the one parameter (post_id) with a basic description. The tool description adds context that the post must be published and that the search is limited to the 500 most recent posts, which aids correct usage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'Get' and the resource 'performance stats for a published post by ID'. It lists specific metrics (views, emails, etc.) and distinguishes from siblings like get_post (retrieves post content) and get_post_comments.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly notes the limitation that Substack has no per-post endpoint and that it searches the 500 most recent published posts. This guides when to use (only for recent posts) and when not (if post not among recent 500). However, it does not name alternative tools for stats beyond that scope.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior5/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Description explains beyond annotations: notes that the returned URL is publicly fetchable, unlisted, not attributed to user. Annotations indicate readOnlyHint=false (write) and openWorldHint=true, which description complements well, no contradiction.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, front-loaded with purpose, every sentence adds value. No unnecessary words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With no output schema, description fully explains return value (hosted URL) and behavioral traits. For a two-parameter upload tool, it is complete and self-contained.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, but description adds clarity on mutual exclusivity and gives examples of data URI prefix and file path format, which goes beyond the schema's descriptions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Upload an image to Substack's CDN' with specific verb and resource. Distinguishes from sibling tools, none of which involve image uploads.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly says to provide exactly one of two mutually exclusive parameters. While it doesn't explicitly state when not to use it, the context of siblings makes it clear this is the only upload tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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