// MCP TOKEN COST

The Slack MCP server costs 37,400 tokens before the first call.

Connect Slack and its 142 tool definitions are loaded into the model's context on every request — 19% of a 200k window spent before your agent does anything.

QUICK ANSWER The Slack MCP server's tool definitions consume 37,400 tokens — 35× the median MCP server (1,075 tokens). A scoped grant exposing only the tools you use cuts that roughly in proportion.

MEASURED FROM SCHEMAS 142 tools · 37,400 tokens · 19% of 200k · 3.7% of 1M Method →

// CONTEXT WINDOW SHARE

What that buys before your agent starts working.

Tool definitions are overhead: they occupy context on every request and compete with your code, documents and conversation history for the same window.

200K WINDOW 19%

1M WINDOW 3.7%

Corpus context: Slack ranks #10 of 1,659 measured MCP servers by definition cost. The median is 1,075 tokens, p90 is 6,119, and the heaviest (Fusionauth) is 183,337 — 92% of a 200k window on its own.

// PER-TOOL BREAKDOWN

Where the 37,400 tokens go.

Each row is one tool definition as a tools/list entry — name, description and input schema — counted with o200k_base. Average: 263 tokens per tool.

Tool	Category	Tokens	% of server
SLACK_SENDS_A_MESSAGE_TO_A_SLACK_CHANNEL	Read	1,409	3.8%
SLACK_SEND_MESSAGE	Write	1,406	3.8%
SLACK_CHAT_POST_MESSAGE	Write	1,403	3.8%
SLACK_SCHEDULE_MESSAGE	Write	911	2.4%
SLACK_SCHEDULES_A_MESSAGE_TO_A_CHANNEL_AT_A_SPECIFIED_TIME	Read	904	2.4%
SLACK_SEARCH_MESSAGES	Read	882	2.4%
SLACK_UPDATES_A_SLACK_MESSAGE	Read	867	2.3%
SLACK_SEARCH_FOR_MESSAGES_WITH_QUERY	Read	862	2.3%
SLACK_REGISTERS_A_NEW_CALL_WITH_PARTICIPANTS	Execute	749	2.0%
SLACK_START_CALL	Execute	744	2.0%
SLACK_SENDS_EPHEMERAL_MESSAGES_TO_CHANNEL_USERS	Read	673	1.8%
SLACK_SEND_EPHEMERAL_MESSAGE	Write	658	1.8%
SLACK_UPDATES_AN_EXISTING_REMOTE_FILE	Write	584	1.6%
SLACK_ADD_A_REMOTE_FILE_FROM_A_SERVICE	Write	494	1.3%
SLACK_INVITE_USER_TO_WORKSPACE	Write	483	1.3%
SLACK_INVITE_USER_TO_WORKSPACE_WITH_OPTIONAL_CHANNEL_INVITES	Write	481	1.3%
SLACK_LIST_CONVERSATIONS	Read	453	1.2%
SLACK_LIST_ACCESSIBLE_CONVERSATIONS_FOR_A_USER	Read	444	1.2%
SLACK_LIST_FILES_WITH_FILTERS_IN_SLACK	Read	443	1.2%
SLACK_UPLOAD_OR_CREATE_A_FILE_IN_SLACK	Write	443	1.2%
SLACK_CUSTOMIZE_URL_UNFURL	Destructive	427	1.1%
SLACK_CUSTOMIZE_URL_UNFURLING_IN_MESSAGES	Read	424	1.1%
SLACK_RETRIEVE_DETAILED_INFORMATION_ABOUT_A_FILE	Read	418	1.1%
SLACK_FETCH_CONVERSATION_HISTORY	Read	404	1.1%
SLACK_EDIT_CANVAS	Write	397	1.1%
SLACK_SET_SLACK_USER_PROFILE_INFORMATION	Write	370	1.0%
SLACK_LIST_ALL_SLACK_TEAM_CHANNELS_WITH_VARIOUS_FILTERS	Read	365	1.0%
SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION	Read	354	0.9%
SLACK_LIST_SCHEDULED_MESSAGES	Read	349	0.9%
SLACK_SEARCH_ALL	Read	349	0.9%
SLACK_LIST_ALL_CHANNELS	Read	346	0.9%
SLACK_LIST_SCHEDULED_MESSAGES_IN_A_CHANNEL	Read	343	0.9%
SLACK_FIND_CHANNELS	Read	342	0.9%
SLACK_FIND_USERS	Read	342	0.9%
SLACK_RETRIEVE_CONVERSATION_MEMBERS_LIST	Read	342	0.9%
SLACK_LIST_CANVASES	Read	305	0.8%
SLACK_CREATE_A_REMINDER	Write	298	0.8%
SLACK_CREATE_CHANNEL_BASED_CONVERSATION	Write	285	0.8%
SLACK_CREATE_A_SLACK_USER_GROUP	Write	284	0.8%
SLACK_FETCH_ITEM_REACTIONS	Read	283	0.8%
SLACK_ADD_REACTION_TO_AN_ITEM	Write	274	0.7%
SLACK_SET_STATUS	Write	269	0.7%
SLACK_UPDATE_AN_EXISTING_SLACK_USER_GROUP	Write	262	0.7%
SLACK_ADD_A_CUSTOM_EMOJI_TO_A_SLACK_TEAM	Write	258	0.7%
SLACK_LIST_USER_REACTIONS	Read	252	0.7%
SLACK_SHARE_REMOTE_FILE_IN_CHANNELS	Read	252	0.7%
SLACK_ADD_A_STAR_TO_AN_ITEM	Write	252	0.7%
SLACK_DELETES_A_MESSAGE_FROM_A_CHAT	Read	248	0.7%
SLACK_LIST_ALL_USERS	Read	248	0.7%
SLACK_UPDATE_SLACK_CALL_INFORMATION	Write	247	0.7%
SLACK_REMOVE_A_STAR_FROM_AN_ITEM	Destructive	246	0.7%
SLACK_ADD_EMOJI	Write	246	0.7%
SLACK_LIST_ALL_SLACK_TEAM_USERS_WITH_PAGINATION	Read	244	0.7%
SLACK_DELETE_A_SCHEDULED_MESSAGE_IN_A_CHAT	Destructive	238	0.6%
SLACK_OPEN_OR_RESUME_DIRECT_OR_MULTI_PERSON_MESSAGES	Write	234	0.6%
SLACK_LIST_SLACK_S_REMOTE_FILES_WITH_FILTERS	Read	232	0.6%
SLACK_LISTS_USER_S_STARRED_ITEMS_WITH_PAGINATION	Read	231	0.6%
SLACK_OPEN_DM	Write	229	0.6%
SLACK_SHARE_A_ME_MESSAGE_IN_A_CHANNEL	Read	221	0.6%
SLACK_REGISTERS_NEW_CALL_PARTICIPANTS	Execute	218	0.6%
SLACK_LIST_REMOTE_FILES	Read	215	0.6%
SLACK_CREATE_CANVAS	Write	215	0.6%
SLACK_LIST_STARRED_ITEMS	Read	212	0.6%
SLACK_UPDATE_USER_GROUP_MEMBERS	Write	207	0.6%
SLACK_ADD_CALL_PARTICIPANTS	Write	203	0.5%
SLACK_LIST_WORKSPACE_USERS	Read	201	0.5%
SLACK_SET_READ_CURSOR_IN_A_CONVERSATION	Write	198	0.5%
SLACK_ADD_AN_EMOJI_ALIAS_IN_SLACK	Write	192	0.5%
SLACK_RETRIEVE_CONVERSATION_INFORMATION	Read	184	0.5%
SLACK_RETRIEVE_MESSAGE_PERMALINK_URL	Read	182	0.5%
SLACK_SET_A_CONVERSATION_S_PURPOSE	Write	178	0.5%
SLACK_START_REAL_TIME_MESSAGING_SESSION	Execute	176	0.5%
SLACK_REGISTER_CALL_PARTICIPANTS_REMOVAL	Write	176	0.5%
SLACK_REMOVE_REACTION_FROM_ITEM	Destructive	175	0.5%
SLACK_INVITE_USER_TO_CHANNEL	Write	171	0.5%
SLACK_REMOVE_A_REMOTE_FILE	Destructive	169	0.5%
SLACK_SET_USER_PROFILE_PHOTO_WITH_CROPPING_OPTIONS	Write	168	0.4%
SLACK_LOOKUP_CANVAS_SECTIONS	Read	166	0.4%
SLACK_UNPIN_ITEM_FROM_CHANNEL	Read	166	0.4%
SLACK_LIST_USER_GROUPS_FOR_TEAM_WITH_OPTIONS	Read	163	0.4%
SLACK_REMOVE_CALL_PARTICIPANTS	Destructive	161	0.4%
SLACK_INVITE_USERS_TO_A_SLACK_CHANNEL	Write	159	0.4%
SLACK_SET_THE_TOPIC_OF_A_CONVERSATION	Write	158	0.4%
SLACK_RENAME_AN_EMOJI	Write	155	0.4%
SLACK_RETRIEVE_USER_PROFILE_INFORMATION	Read	150	0.4%
SLACK_SET_PROFILE_PHOTO	Write	150	0.4%
SLACK_DISABLE_AN_EXISTING_SLACK_USER_GROUP	Destructive	147	0.4%
SLACK_RENAME_A_SLACK_CHANNEL	Write	147	0.4%
SLACK_INITIATES_CHANNEL_BASED_CONVERSATIONS	Read	146	0.4%
SLACK_REMOVE_A_USER_FROM_A_CONVERSATION	Destructive	144	0.4%
SLACK_LIST_ALL_USERS_IN_A_USER_GROUP	Read	144	0.4%
SLACK_GET_USER_PRESENCE_INFO	Read	143	0.4%
SLACK_ENABLE_A_SPECIFIED_USER_GROUP	Write	142	0.4%
SLACK_PINS_AN_ITEM_TO_A_CHANNEL	Read	138	0.4%
SLACK_RETRIEVE_DETAILED_USER_INFORMATION	Read	135	0.4%
SLACK_FETCH_CURRENT_TEAM_INFO_WITH_OPTIONAL_TEAM_SCOPE	Read	131	0.4%
SLACK_RENAME_A_CONVERSATION	Write	131	0.4%
SLACK_DELETE_A_COMMENT_ON_A_FILE	Destructive	130	0.3%
SLACK_CREATE_CHANNEL	Write	129	0.3%
SLACK_RETRIEVE_TEAM_PROFILE_DETAILS	Read	128	0.3%
SLACK_LEAVE_A_CONVERSATION	Read	127	0.3%
SLACK_FETCH_TEAM_INFO	Read	125	0.3%
SLACK_CLOSE_DM_OR_MULTI_PERSON_DM	Write	122	0.3%
SLACK_MANUALLY_SET_USER_PRESENCE	Write	122	0.3%
SLACK_MARK_REMINDER_AS_COMPLETE	Write	120	0.3%
SLACK_RETRIEVE_CURRENT_USER_DND_STATUS	Read	119	0.3%
SLACK_END_A_CALL_WITH_DURATION_AND_ID	Write	119	0.3%
SLACK_LISTS_PINNED_ITEMS_IN_A_CHANNEL	Read	116	0.3%
SLACK_ARCHIVE_A_SLACK_CONVERSATION	Write	116	0.3%
SLACK_JOIN_AN_EXISTING_CONVERSATION	Read	115	0.3%
SLACK_FIND_USER_BY_EMAIL_ADDRESS	Read	102	0.3%
SLACK_DELETE_A_FILE_BY_ID	Destructive	100	0.3%
SLACK_RETRIEVE_REMOTE_FILE_INFO_IN_SLACK	Read	100	0.3%
SLACK_REVOKE_PUBLIC_SHARING_ACCESS_FOR_A_FILE	Destructive	95	0.3%
SLACK_DELETE_USER_PROFILE_PHOTO	Destructive	94	0.3%
SLACK_FETCH_WORKSPACE_SETTINGS_INFORMATION	Read	92	0.2%
SLACK_RETRIEVE_CALL_INFORMATION	Read	91	0.2%
SLACK_UNARCHIVE_A_PUBLIC_OR_PRIVATE_CHANNEL	Write	91	0.2%
SLACK_DELETE_A_PUBLIC_OR_PRIVATE_CHANNEL	Destructive	90	0.2%
SLACK_DELETE_A_SLACK_REMINDER	Destructive	90	0.2%
SLACK_GET_CHANNEL_CONVERSATION_PREFERENCES	Read	87	0.2%
SLACK_ACTIVATE_OR_MODIFY_DO_NOT_DISTURB_DURATION	Write	86	0.2%
SLACK_FETCH_BOT_USER_INFORMATION	Read	85	0.2%
SLACK_FETCH_DND_STATUS_FOR_MULTIPLE_TEAM_MEMBERS	Read	84	0.2%
SLACK_GET_REMOTE_FILE	Read	83	0.2%
SLACK_GET_REMINDER_INFORMATION	Read	82	0.2%
SLACK_ARCHIVE_A_PUBLIC_OR_PRIVATE_CHANNEL	Write	79	0.2%
SLACK_ENABLE_PUBLIC_SHARING_OF_A_FILE	Write	78	0.2%
SLACK_END_USER_DO_NOT_DISTURB_SESSION	Read	70	0.2%
SLACK_REVERSE_A_CONVERSATION_S_ARCHIVAL_STATUS	Read	70	0.2%
SLACK_GET_TEAM_DND_STATUS	Read	67	0.2%
SLACK_SET_DND_DURATION	Write	67	0.2%
SLACK_GET_CANVAS	Read	64	0.2%
SLACK_RETRIEVE_A_USER_S_IDENTITY_DETAILS	Read	63	0.2%
SLACK_LIST_TEAM_CUSTOM_EMOJIS	Read	55	0.1%
SLACK_DELETE_CANVAS	Destructive	54	0.1%
SLACK_END_USER_SNOOZE_MODE_IMMEDIATELY	Read	53	0.1%
SLACK_UNARCHIVE_CHANNEL	Write	53	0.1%
SLACK_LIST_USER_REMINDERS_WITH_DETAILS	Read	50	0.1%
SLACK_LIST_REMINDERS	Read	45	0.1%
SLACK_CLEAR_STATUS	Destructive	39	0.1%
SLACK_END_SNOOZE	Read	34	0.1%

Computed over 142 of 143 catalogued tools — the remainder have no published input schema, so the true total is slightly higher.

// SCOPED GRANT

Most agents use a handful of these tools. They pay for all 142.

A PolicyLayer grant exposes only the tools you allow — ungranted definitions are filtered out of the tool list, so they never enter the context window. Estimates below assume typical-weight tools (263 tokens each).

Grant scope	Definition cost	Reduction
All 142 tools (no gateway)	37,400 tokens	—
3 granted tools	~790 tokens	−98%
5 granted tools	~1,317 tokens	−96%
10 granted tools	~2,634 tokens	−93%

Model your own stack in the token-cost calculator, or see the Slack policy for what a sensible grant looks like.

//FAQ

Slack token-cost questions.

How many tokens does the Slack MCP server use?+

Its 142 tool definitions total 37,400 tokens — 19% of a 200k context window — measured with tiktoken o200k_base over the serialised tools/list payload. Exact counts vary slightly by client and model.

Why does Slack consume tokens before I send a message?+

MCP clients load every connected server's tool definitions — name, description, and input schema — into the model's context so it knows what it can call. That payload is charged against your context window on every request, whether or not a tool is used.

How do I reduce Slack's token usage?+

Expose fewer tools. A PolicyLayer grant scopes Slack to only the tools you allow — ungranted definitions are filtered out of the tool list, so they never enter the context window. A grant of 3 typical tools costs roughly 790 tokens, a 98% reduction.

Does deferred tool loading fix this?+

Partially, in some clients. Claude Code defers MCP tool schemas behind a tool-search step by default, and VS Code has experimental grouping — but you still pay tokens per search and reload, and Cursor, Windsurf and Gemini CLI load definitions upfront. Reducing the exposed tool set cuts the cost in every client.

// METHOD & REVIEW

How these numbers were measured.

01

Serialisation

Each tool is serialised as a tools/list entry — name, description, input schema — from the schemas in the PolicyLayer scan database. Clients differ slightly in framing, so treat counts as close estimates.

02

Tokeniser

tiktoken o200k_base (GPT-4o/o-series). Anthropic's current tokeniser isn't published, so Claude's exact counts will differ; for English text and JSON schemas the totals are close enough to treat these as estimates.

03

Deferred loading

Some clients now defer schema loading (Claude Code's tool search; VS Code experimental grouping). You still pay per search and reload — and Cursor, Windsurf and Gemini CLI load everything upfront.

Computed 05-06-2026 from the PolicyLayer scan database over 142 of 143 catalogued Slack tools. Counts refresh with every site build.