substack-mcp
Syncs recent posts from Substack publications, caches metadata and markdown locally, and provides tools for listing, fetching post chunks, and marking posts as summarized for daily summary generation. Supports paid subscriptions the user has access to.
Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type
@followed by the MCP server name and your instructions, e.g., "@substack-mcpfetch recent Substack posts and list unsummarized ones"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
mcp-substack
Local MCP server for giving Copilot access to Substack posts that your own reader account is allowed to view, including paid posts from your subscriptions.
The main workflow is daily summary generation:
Sync recent posts from priority Substack publications.
Cache metadata and markdown locally.
Let Copilot list unsummarized posts.
Let Copilot fetch long posts in chunks.
Mark summarized posts so they do not repeat tomorrow.
Safety Boundary
This server uses only your own authenticated Substack session.
It does not:
read your normal Chrome profile
read Chrome Keychain-backed cookie storage
store your Substack password
bypass paywalls
share paid content outside your machine
Authentication is handled through a dedicated Playwright browser profile:
~/Library/Application Support/mcp-substack/browser-profile/Cached article data is stored locally:
~/Library/Application Support/mcp-substack/substack.dbLocal config is stored at:
~/Library/Application Support/mcp-substack/config.jsonRelated MCP server: Substack MCP
Requirements
macOS
Node.js 26 or newer recommended, because this project uses Node's built-in
node:sqlitenpm
Install
cd ~/path/to/substack-mcp
npm install
npx playwright install chromium
npm run buildFirst Login
Open the dedicated Substack browser profile and log in once:
npm run spike -- login 300If you are already logged in, the browser may open briefly and close.
Check login status:
npm run spike -- statusExpected result:
{
"loggedIn": true
}Priority Publications
You can optionally configure a small set of priority publications for daily summary runs. This is useful when you subscribe to many publications but only want a subset in the default summary.
Set or reset priority publications with your own publication URLs:
npm run spike -- config-priority \
https://example-newsletter.substack.com \
https://example.comShow current config:
npm run spike -- config-showLocal Sync Commands
Sync only priority publications:
npm run spike -- sync-priority 3 5This means:
last 3 days
up to 5 recent posts per priority publication
fetch full article bodies into the local cache
List cached unsummarized posts:
npm run spike -- cache-list 20Useful diagnostics:
npm run spike -- discover
npm run spike -- list-posts https://example-newsletter.substack.com 5MCP Server
Build and run the MCP server over stdio:
npm run build
npm startExample MCP client config:
{
"servers": {
"substack": {
"command": "node",
"args": [
"/absolute/path/to/substack-mcp/dist/server.js"
]
}
}
}Daily Copilot Workflow
Recommended tool sequence:
substack_sync_recent{ "days": 3, "limitPerPublication": 5, "priorityOnly": true, "fetchContent": true }substack_list_posts{ "summarized": false, "limit": 20 }For each post to summarize, call
substack_get_post_chunks.{ "postKeyOrUrl": "<postKey from substack_list_posts>", "maxChars": 8000 }After generating the daily summary, call
substack_mark_summarized.{ "postKeyOrUrls": ["<postKey>", "<postKey>"], "summaryDate": "2026-06-30" }
MCP Tools
substack_loginOpens the dedicated browser profile and waits for Substack login.
substack_sync_statusShows app paths, config, and login status.
substack_config_showShows local config.
substack_config_set_priority_publicationsSets priority publication URLs.
substack_config_set_defaultsSets default sync window and per-publication limit.
substack_discover_subscriptionsDiscovers publications from the authenticated reader account.
substack_sync_recentSyncs recent posts into SQLite.
substack_list_postsLists cached post metadata. This does not return full bodies.
substack_get_cached_postReturns one cached post with markdown.
substack_get_post_chunksReturns one cached post split into bounded markdown chunks.
substack_mark_summarizedMarks posts as included in a daily summary.
substack_list_recent_postsDiagnostic tool for listing recent posts from one publication.
substack_get_postDiagnostic tool for live-fetching one post as markdown.
Verification Status
Current verified behavior:
dedicated browser profile login works
subscription discovery works
paid full text works for authorized subscriptions
priority-only sync works
SQLite cache stores metadata and markdown
chunking works for long articles
npm run typecheckpassesnpm run buildpasses
Troubleshooting
Browser Opens and Closes Quickly
This usually means the dedicated profile is already logged in and the login check succeeded.
Run:
npm run spike -- statusPlaywright Browser Missing
Run:
npx playwright install chromiumSubstack Returns 429
Substack may rate-limit repeated sync attempts. Wait a few minutes and retry with a smaller window:
npm run spike -- sync-priority 3 2Paid Post Shows Preview Only
Check that the dedicated profile is logged into the account with the paid subscription:
npm run spike -- statusThen test the publication directly:
npm run spike -- list-posts https://example-newsletter.substack.com 5Reset Local State
The local data lives outside the repository:
~/Library/Application Support/mcp-substack/Remove only the files you intend to reset. Deleting browser-profile/ requires
logging into Substack again. Deleting substack.db removes cached articles and
summary state.
Available Tools
13 toolssubstack_config_set_defaultsSet Substack Sync DefaultsC
Set default sync window and per-publication post limit.
| Name | Required | Description | Default |
|---|---|---|---|
| defaultSyncDays | Yes | ||
| defaultFetchContent | No | ||
| defaultLimitPerPublication | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description must disclose behavioral traits. It only states that defaults are set, with no mention of side effects, permissions required, or mutability. For a configuration mutation tool, this is insufficient.
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?
The description is a single clear sentence with no extraneous words. It is appropriately short and front-loaded with the key action.
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?
Given three parameters, no output schema, and no annotations, the description leaves the agent without understanding return values, side effects, or how configuration changes persist. It is not complete enough for reliable use.
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 0%, yet the description adds no information about the parameters. It does not explain what 'defaultSyncDays' or 'defaultLimitPerPublication' mean, nor how 'defaultFetchContent' affects behavior. The schema provides constraints but lacks semantics.
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?
The description clearly states the tool sets defaults for sync window and per-publication post limit. It uses the verb 'Set' and identifies the specific resources. While it doesn't explicitly distinguish from sibling tool 'substack_config_set_priority_publications', the purpose is clear enough for selection.
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?
No guidance is provided on when to use this tool versus alternatives like 'substack_config_show' or 'substack_config_set_priority_publications'. There are no prerequisites or contextual usage instructions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_config_set_priority_publicationsSet Priority Substack PublicationsB
Set publication URLs that should be synced first or exclusively for daily summaries.
| Name | Required | Description | Default |
|---|---|---|---|
| publicationUrls | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full burden for behavioral disclosure. It states that URLs will be synced 'first or exclusively', but fails to detail whether this replaces or merges existing priorities, if the operation is reversible, or any side effects on other syncing behavior. The behavioral insight is minimal.
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?
The description is a single, well-structured sentence that conveys the essential information without extraneous words. It is appropriately sized and front-loaded with the key action and resource.
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?
Given the tool's simplicity (1 parameter, no output schema, no annotations), the description adequately states the purpose and effect. However, it lacks details about whether the operation is additive or replaces existing settings, any maximum URL count, or how it interacts with other config tools. This leaves minor gaps for an agent.
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 0%, so the description must compensate. It adds context that the URLs are used for daily summaries and priority syncing, but does not explain URL format constraints beyond the schema's 'uri' format, nor specify if multiple URLs are additive or exclusive. It provides some semantic value but is not comprehensive.
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?
The description clearly states the tool's purpose: setting publication URLs to be synced first or exclusively for daily summaries. The verb 'Set' and specific resource 'publication URLs' make the action unambiguous. It effectively distinguishes from sibling tools like 'substack_config_set_defaults' by focusing on priority/exclusivity.
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 provides no guidance on when to use this tool versus alternatives such as 'substack_config_set_defaults' or 'substack_discover_subscriptions'. It does not mention prerequisites, exclusions, or context for invocation. The usage is only implied through the tool's purpose.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_config_showShow Substack MCP ConfigB
Show local mcp-substack configuration.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries full burden for behavioral disclosure. It does not state that the tool is read-only, has no side effects, or what data it accesses. This is a significant gap.
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?
The description is a single concise sentence. It is front-loaded and efficient, though it could be slightly more informative without becoming verbose.
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?
Given the tool's simplicity (no parameters, no output schema, no annotations), the description is adequate but lacks detail on what 'configuration' includes or what the output format is. Slightly incomplete for a tool with no other documentation.
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?
The tool has zero parameters, so the description adds meaning by specifying 'local mcp-substack configuration', indicating the scope of what is shown. Baseline is 4 for no parameters.
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?
The description clearly states the tool shows the local mcp-substack configuration. The verb 'Show' and resource 'configuration' are specific, and the tool's name and title align. It is distinct from sibling config tools like 'substack_config_set_defaults'.
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 provides no guidance on when to use this tool versus alternatives. It does not mention prerequisites, when it is appropriate, or when to avoid it. For a simple read-only tool, some context could be helpful.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_discover_subscriptionsDiscover Substack SubscriptionsB
Use the authenticated dedicated browser profile to discover subscribed publications.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description should disclose critical behavioral traits like side effects, authentication requirements, and output format. It only mentions using an authenticated profile, but does not clarify if the tool is read-only, whether it modifies data, or what triggers the 'discovery' process.
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?
The description is a single concise sentence, which is efficient. However, it could be slightly more structured to include context about expected results without becoming verbose.
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?
Given no output schema, the description should explain return values or behavior beyond the action. It does not state what 'discover' returns (e.g., list of publication names, URLs, or metadata), leaving a significant gap for the agent.
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?
The tool has zero parameters, so the description adds no param-specific meaning. According to the rule, 0 parameters yields a baseline of 4; the schema coverage is 100% and no additional param info is needed.
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?
The description clearly states the tool discovers subscribed publications using an authenticated browser profile, which is a specific verb-resource pair. It is distinct from sibling tools, none of which mention 'discover' or 'subscriptions' directly.
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?
No guidance is provided on when to use this tool versus alternatives, such as listing posts or syncing. The description does not mention prerequisites or context for invocation.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_get_cached_postGet Cached Substack PostC
Return one cached post with markdown content.
| Name | Required | Description | Default |
|---|---|---|---|
| postKeyOrUrl | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description should disclose behavioral traits. It only states the output format. It does not mention if the cache can be stale, what happens on cache miss, required permissions, or side effects. This is insufficient for a tool with zero annotation coverage.
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?
The description is one short sentence, front-loading the key action and output. It is concise with no wasted words. However, it could be slightly expanded to include critical details without losing conciseness.
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 simple tool with one parameter and no output schema, the description is minimal. Given multiple sibling tools for getting posts, more context on caching behavior and relationship to other get tools is needed. The description feels incomplete for an AI agent to select correctly.
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?
The single parameter 'postKeyOrUrl' is named descriptively, but the description adds no further clarification. Since schema description coverage is 0%, the description should explain the expected format (e.g., a URL or a key). It does not, leaving ambiguity.
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?
The description clearly states the tool returns one cached post with markdown content. It specifies the verb 'return', the resource 'cached post', and the output format. However, it does not differentiate from sibling tools like 'substack_get_post' beyond the name.
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?
No guidance is provided on when to use this tool versus alternatives like 'substack_get_post' or 'substack_get_post_chunks'. The description lacks context about cache semantics or when a cached version is preferable.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_get_postGet Substack PostB
Fetch one Substack post through the authenticated browser profile and return markdown.
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It mentions 'authenticated browser profile' implying a prerequisite, but does not disclose side effects like marking as read or rate limiting. The output format 'markdown' is stated.
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?
Single sentence, front-loaded with key information, no wasted words.
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?
Adequate for a simple tool with one parameter and no output schema. However, missing error conditions and explicit prerequisite (login status). Could clarify relationship to substack_get_cached_post.
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 0%, but the single 'url' parameter is self-explanatory. The description adds minimal meaning beyond the schema, only implying the URL points to a Substack post.
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?
The description clearly states the verb ('Fetch'), resource ('one Substack post'), and method ('through authenticated browser profile, return markdown'). It distinguishes from sibling tools like substack_get_cached_post and substack_list_posts.
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?
No guidance on when to use this tool versus alternatives like substack_get_cached_post or substack_list_posts. No prerequisites mentioned, such as requiring prior login via substack_login.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_get_post_chunksGet Cached Substack Post ChunksC
Return bounded markdown chunks for one cached post.
| Name | Required | Description | Default |
|---|---|---|---|
| maxChars | No | ||
| postKeyOrUrl | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of disclosing behavioral traits. It mentions 'bounded markdown chunks' but does not explain how chunks are delimited, whether they are ordered, or what happens if the post is not cached. No information about errors, rate limits, or side effects is given.
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?
The description is extremely concise, consisting of one short sentence. While this is efficient, it lacks structure and fails to convey important details. It could be improved by adding a brief explanation of chunking and parameter usage without becoming verbose.
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?
Given the absence of annotations and output schema, the description is insufficiently complete. It does not cover return format, error conditions, or relationship to sibling tools. For a tool with only two parameters, more context is needed to enable correct usage.
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 0%, yet the description adds no meaning to the parameters. It does not explain what 'postKeyOrUrl' accepts (e.g., format examples) or how 'maxChars' affects the chunking behavior. The parameters are left entirely undocumented beyond the schema's basic type and constraints.
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?
The description states that the tool returns 'bounded markdown chunks for one cached post', which clearly indicates the action and resource. However, it does not explicitly distinguish itself from the sibling tool 'substack_get_cached_post', which likely returns the entire post. The term 'bounded' is vague but implies chunking.
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?
No guidance is provided on when to use this tool over alternatives like 'substack_get_cached_post' or 'substack_get_post'. The description does not specify any prerequisites, such as the post needing to be cached, nor does it mention when not to use this tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_list_postsList Cached Substack PostsB
List cached posts, optionally filtered to unsummarized posts and a date range.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | ||
| since | No | ||
| until | No | ||
| summarized | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It correctly labels the operation as listing (read-only) but does not disclose details such as rate limits, pagination behavior, or whether it returns full post content. The description is not misleading but is minimal.
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?
The description is a single sentence that efficiently conveys the core functionality. Every word serves a purpose, and there is no unnecessary information.
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?
Given the complexity (4 parameters, no output schema, no annotations, many sibling tools), the description is too minimal. It fails to explain what 'cached' means, differentiate from similar tools, or describe the return format and ordering. An agent would need additional context to use this tool effectively.
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 0%, so the description must compensate. It mentions filtering by unsummarized posts and date range, which partially clarifies the 'summarized' and 'since'/'until' parameters. However, it omits the 'limit' parameter and does not specify the date format, leaving significant ambiguity.
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?
The description clearly states it lists cached posts with optional filtering. However, it does not explicitly distinguish from sibling tools like substack_list_recent_posts, which might cause confusion about the difference between 'cached' and 'recent' posts.
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?
No guidance is provided on when to use this tool versus alternatives. There is no mention of prerequisites, context, or when not to use it. The description implies usage for cached posts but lacks explicit direction.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_list_recent_postsList Recent Substack PostsB
List recent posts for a publication URL. This is the spike path before cache-backed sync.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | ||
| publication | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description must disclose behavioral traits. It mentions 'spike path' indicating a direct API call without caching, but does not specify side effects, rate limits, read-only nature, or return format, leaving significant gaps.
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 concise sentences, front-loaded with core action. The second sentence adds useful context without fluff. Every word 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?
Given the complexity (nested object, no output schema, no annotations), the description is too brief. It fails to explain optional nested fields or return value, leaving the agent underinformed for correct invocation.
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 0%, so the description must compensate. It clarifies the required 'publication.url' parameter as the publication URL, and implies 'limit' controls number of posts, but ignores other nested object fields (id, name, subdomain, customDomain) with no explanation.
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?
The description clearly states the tool lists recent posts for a publication URL, using verb+resource. It adds context with 'spike path before cache-backed sync', which hints at its purpose but does not explicitly differentiate from sibling 'substack_list_posts'.
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?
Implies usage via 'spike path before cache-backed sync', suggesting it's for immediate uncached data, but does not explicitly state when to use versus alternatives like 'substack_list_posts' or 'substack_sync_recent'.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_loginSubstack LoginB
Open a dedicated local browser profile and wait for the user to log into Substack.
| Name | Required | Description | Default |
|---|---|---|---|
| timeoutSeconds | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided, so description carries full burden. It describes opening a browser and waiting for user login, but fails to disclose what happens after login, whether login state persists, or any side effects like requiring a fresh browser profile.
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?
The description is a single, front-loaded sentence with no wasted words. However, it could include more detail without becoming verbose.
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 login tool with one optional parameter and no output schema, the description lacks critical context such as expected outcomes, error handling, and whether the tool blocks or returns. Leaves significant gaps for an AI agent.
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 0%, and the description does not mention the timeoutSeconds parameter at all. The parameter has no description in the schema, and the tool description fails to add meaning or usage context.
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?
The description clearly states the action (Open a dedicated local browser profile and wait for the user to log into Substack). It distinguishes from siblings which are about config, posts, sync, etc., making it unique for authentication.
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 implies usage for initial login but does not explicitly state when to use this tool versus alternatives. No exclusions or prerequisites are mentioned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_mark_summarizedMark Substack Posts SummarizedC
Mark cached posts as included in a daily summary.
| Name | Required | Description | Default |
|---|---|---|---|
| summaryDate | No | 2026-06-30 | |
| postKeyOrUrls | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description must fully disclose behavioral traits. It only states the action without explaining what 'mark' entails (e.g., mutating a database, idempotency, side effects, required prior caching, or failure scenarios). This is insufficient for safe invocation.
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?
The description is a single concise sentence with no wasted words. It is front-loaded and efficient.
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?
Given the absence of annotations and output schema, the description is severely incomplete. It lacks parameter semantics, behavioral detail, return value information, and any guidance on when to use the tool. An agent cannot make an informed decision to invoke this tool based on the current description.
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 0%, and the description adds no explanation for either parameter (summaryDate, postKeyOrUrls). The agent cannot infer the purpose, format, or constraints of these parameters from the description alone.
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?
The description 'Mark cached posts as included in a daily summary' clearly states the verb (mark), resource (cached posts), and outcome (included in a daily summary). It distinguishes from sibling tools which are focused on configuration, retrieval, or syncing. However, the scope of 'cached posts' could be more precise.
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 provides no guidance on when to use this tool versus alternatives, no prerequisites, and no context about the daily summary workflow. The agent must infer usage from the name alone.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_sync_recentSync Recent Substack PostsC
Discover subscriptions, sync recent posts, fetch bodies, and save them in the local cache.
| Name | Required | Description | Default |
|---|---|---|---|
| days | No | ||
| fetchContent | No | ||
| priorityOnly | No | ||
| maxPublications | No | ||
| publicationUrls | No | ||
| useConfigPriority | No | ||
| limitPerPublication | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations present; description fails to disclose behavioral traits such as authentication requirements, network calls, or side effects. The brief description does not add transparency beyond the tool name.
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?
The description is a single sentence, but it is a run-on listing multiple actions without structuring. It is concise but lacks front-loading of primary purpose.
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?
Given 7 parameters, no output schema, and no annotations, the description is highly incomplete. It fails to provide adequate context for effective tool use.
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 0% and the description does not explain any of the 7 parameters. It provides no additional meaning beyond the schema, failing to help an agent understand parameter usage.
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?
Description lists multiple actions (discover, sync, fetch, save) without a single clear purpose. While not a tautology, it is vague and does not distinguish from sibling tools like substack_discover_subscriptions or substack_list_recent_posts.
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?
No guidance on when to use this tool versus alternatives. Description does not provide context for selection among many sibling tools.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
substack_sync_statusSubstack Sync StatusA
Check the dedicated Substack browser profile path and current login status.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must disclose all behavioral traits. It implies a read-only check but does not explain whether it makes network requests, caches results, or if it might require a browser profile to exist. Minimal but not misleading.
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?
A single sentence that conveys two clear pieces of information without any filler. Every word 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?
Given the tool's simplicity (no params, no output schema), the description is adequate but lacks detail about the return format. An agent cannot know what data it will receive, which is a gap for a 'check' tool.
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?
No parameters exist; schema coverage is 100%. Baseline score of 4 applies since the description adds no redundant parameter info.
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?
The description clearly states it checks the 'dedicated Substack browser profile path' and 'current login status,' using specific nouns. No sibling tool duplicates this function, making it unambiguous.
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?
No guidance on when to use this tool vs sibling tools. For instance, it does not mention that this is a prerequisite before other operations or that it should be used after login failures. It simply states what it does.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
TDQS
All tools have clearly distinct purposes. Even the post retrieval tools (get_cached_post, get_post, get_post_chunks) are well-separated by cache vs live vs chunked output. No overlapping functionality.
All tools follow a consistent verb_noun pattern with the 'substack_' prefix. Verbs are imperative and clear (set, show, discover, get, list, login, mark, sync), and nouns are specific and descriptive.
13 tools cover the core domain of Substack configuration, authentication, subscription discovery, post retrieval, listing, syncing, and summarization. The count is well-scoped without being overwhelming or sparse.
The tool set covers the primary workflows for syncing and summarizing Substack content. Minor gaps exist, such as no tools for individual subscription management (unsubscribe) or content deletion, but the core operations are fully supported.
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