sem

Name: sem
Author: Ataraxy Labs Inc.

Entity-level diff, impact, call-graph and blame queries over a local Git repo for coding agents

By Ataraxy Labs Inc. Rust Local · stdio, Streamable HTTP Developer tools Git and code hosting

GitHub npm Website

73 popularity score ★ 3.4k ↓ 5.8k/wk

Connect your client

Local (once it is running)

Add in one click

Add to Cursor Add to VS Code Add to LM Studio Add to Goose

Opens the app, which asks before it adds the server. Then replace each <NAME> in its settings with your value.

Or add it by command or config

Claude CodeTerminal

claude mcp add --transport http sem http://127.0.0.1:8765/mcp --header 'Authorization: Bearer <SEM_MCP_HTTP_TOKEN>'

Cursor~/.cursor/mcp.json

{
  "mcpServers": {
    "sem": {
      "url": "http://127.0.0.1:8765/mcp",
      "headers": {
        "Authorization": "Bearer <SEM_MCP_HTTP_TOKEN>"
      }
    }
  }
}

VS Code.vscode/mcp.json

{
  "servers": {
    "sem": {
      "type": "http",
      "url": "http://127.0.0.1:8765/mcp",
      "headers": {
        "Authorization": "Bearer <SEM_MCP_HTTP_TOKEN>"
      }
    }
  }
}

Codex~/.codex/config.toml

[mcp_servers.sem]
url = "http://127.0.0.1:8765/mcp"
http_headers = { "Authorization" = "Bearer <SEM_MCP_HTTP_TOKEN>" }

Gemini CLITerminal

gemini mcp add --scope user --transport http --header 'Authorization: Bearer <SEM_MCP_HTTP_TOKEN>' sem http://127.0.0.1:8765/mcp

Local (npm)

Add in one click

Add to Cursor Add to VS Code Add to LM Studio Add to Goose

Opens the app, which asks before it adds the server.

Or add it by command or config

Claude CodeTerminal

claude mcp add sem -- npx -y @ataraxy-labs/sem mcp

Claude Desktopclaude_desktop_config.json

{
  "mcpServers": {
    "sem": {
      "command": "npx",
      "args": [
        "-y",
        "@ataraxy-labs/sem",
        "mcp"
      ]
    }
  }
}

Cursor~/.cursor/mcp.json

{
  "mcpServers": {
    "sem": {
      "command": "npx",
      "args": [
        "-y",
        "@ataraxy-labs/sem",
        "mcp"
      ]
    }
  }
}

VS Code.vscode/mcp.json

{
  "servers": {
    "sem": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "@ataraxy-labs/sem",
        "mcp"
      ]
    }
  }
}

Codex~/.codex/config.toml

[mcp_servers.sem]
command = "npx"
args = ["-y", "@ataraxy-labs/sem", "mcp"]

Gemini CLITerminal

gemini mcp add --scope user sem npx -- -y @ataraxy-labs/sem mcp

Settings 6

Set together: http
`SEM_REPO`	Optional: Absolute path to the repository root when the client does not start sem inside it; required for the HTTP preview.
`SEM_MCP_HTTP_TOKEN` secret	Optional: Bearer token of at least 32 printable characters; the HTTP preview will not start without it. For sem mcp --http.
`SEM_MCP_NO_SHARED`	Optional: Set to any value to run a standalone process instead of joining the shared per-checkout process.
`SEM_NO_INDEX`	Optional: Set to skip the on-disk query index and compute answers directly.
`SEM_TELEMETRY`	Optional: Telemetry mode: off, local (count on this machine only) or on (upload). Default `local`.
`SEM_NO_TELEMETRY`	Optional: Set to 1 to force telemetry off; DO_NOT_TRACK=1 and SEM_NO_NETWORK=1 do the same.

What it does

sem is a Rust command-line tool from Ataraxy Labs. It parses source code with tree-sitter and treats each function, method and class as a named unit, so a change shows up as "this function was modified" rather than "these lines changed". The README counts 32 supported languages. Running `sem mcp` starts the same binary as an MCP server over stdio.

The server lists eight tools. They find where an entity is defined, plus its callers, references, or source with surrounding context. They also search text, list what depends on an entity and which tests reach it, run the project's checkers or one given build or test command and return pass, fail or could not decide, build a review summary for a commit range, diff entities between two refs, draw entity, module or data-flow graphs, and trace an entity's history or blame a file. Older tool names (`sem_entities`, `sem_context`, `sem_callers`, `sem_log`, `sem_blame`) still answer when called but are hidden from the tool list. When started with `sem mcp --review`, it also lists four tools that attach the agent to a code review on Ataraxy Labs' cloud service.

Since 0.28.0 there is also a Streamable HTTP preview, started with `sem mcp --http 127.0.0.1:<PORT>`. It serves only `sem_find` and `sem_grep` for one repository named by `SEM_REPO`, binds to loopback addresses only, and refuses to start unless `SEM_MCP_HTTP_TOKEN` holds a token of at least 32 printable characters (crates/sem-mcp/src/http.rs at v0.28.1). Clients send that token as a bearer header; requests are capped at 1 MiB.

Over stdio the server finds its repository from an absolute file path passed to a tool, then from `SEM_REPO`, then from the working directory (crates/sem-mcp/src/server.rs at v0.28.1) (not in the README). On macOS and Linux, clients in the same checkout share one background process, which takes at most 64 clients (crates/sem-mcp/src/shared.rs) and exits after ten idle minutes.

What it needs

Runtime	Node.js
Runs on	macOS, Windows, Linux
Also	The sem binary, which the npm wrapper's postinstall step downloads A local Git repository to work on

Besides the npm wrapper, sem installs by script, Homebrew (sem-cli), winget, Scoop or cargo (sem-cli); building with cargo needs Rust 1.89 or later. Bun users must run `bun pm trust @ataraxy-labs/sem` so the postinstall step can fetch the binary. Start the client inside the repository or set SEM_REPO. The HTTP preview is started by hand: set SEM_REPO and SEM_MCP_HTTP_TOKEN, run `sem mcp --http 127.0.0.1:8765`, and point the client at http://127.0.0.1:8765/mcp with an `Authorization: Bearer <token>` header. Review mode needs an Ataraxy Labs cloud account (`sem cloud login`).

Limits

Not covered One repository per connection: absolute paths into another repository are refused, so each repository needs its own MCP entry
Platform Windows has no shared process; each client runs its own standalone stdio server (named-pipe sharing is not implemented)
Limit The shared process shares read caches only; it gives no write isolation or lock between agents
Early release The Streamable HTTP endpoint is a preview: loopback only, sem_find and sem_grep only, no OAuth; its docs say not to expose it to the internet
Size cap HTTP preview: requests limited to 1 MiB and eight concurrent requests; indexing CPU and memory are not bounded
Not covered The review tools appear only in `sem mcp --review` sessions
Limit GNU Parallel also installs a /usr/bin/sem; the two clash on PATH unless an alias or PATH order picks the right one

It cannot work across repositories over one connection: absolute paths into another repository are refused, so each repository needs its own MCP connection. On Windows there is no shared process; each client runs its own standalone stdio server. The shared process shares read caches only and gives no write isolation between agents. GNU Parallel also ships a /usr/bin/sem, and the two names clash on PATH; the README suggests an alias or putting cargo's bin directory first. The review tools appear only in `sem mcp --review` sessions.

Who it suits

Suits developers whose coding agents work in local Git repositories and need precise answers: who calls a function, what a change touches, which tests to run. sem answers these from a parsed dependency graph instead of text search, and the default tools run on your machine with no account. Clients that cannot launch stdio servers can use the HTTP preview, but only for find and grep and only on loopback or through an SSH tunnel. Developers who want search across many repositories in one connection, or a hosted endpoint, need something else; Windows users get no shared process.

Tools 12

8 only read, 4 change things. A ? marks an optional parameter.

sem_find: Locate an entity's definition; mode callers, refs or context adds callers, references or source with neighboursquery?: stringqueries?: arraymode?: stringin?: stringfile?: stringlimit?: integertoken_budget?: integerhops?: integerheaders?: booleantext?: stringintent?: stringfiles?: arraylines?: stringfresh?: booleanformat?: string
sem_grep: Regex or literal text search across the repository's files, returning file:line hitspattern?: stringpatterns?: arraycase_insensitive?: booleanin?: stringbodies?: booleantoken_budget?: integerformat?: string
sem_impact: List what depends on an entity, what it depends on, and the tests that reach itfile_path: stringentity_name: stringmode?: stringno_default_excludes?: boolean
sem_check changes: Run the project's checkers, or one given build or test command, and give a pass, fail or undecided verdictbase?: stringcheckers?: arraypromises?: booleanrun?: stringat_base?: boolean
sem_certify: Produce a review summary for a commit range: changed entities, untouched callers, covering testsrange: stringarch?: booleanformat?: string
sem_diff: Show which functions, classes and methods changed between two refs or in the working treebase_ref?: stringtarget_ref?: stringfile_path?: string
sem_graph: Return the entity, module, data-flow or system graphlayer?: stringoperation?: array
sem_history: Trace how an entity changed over commits, list hotspots, or blame a fileentity_name?: stringfile_path?: stringblame?: booleanlimit?: integer
join_review changes: Review mode only: attach the session to a cloud code review as a listenerdiff_id: string
wait_for_branch changes: Review mode only: wait for and claim the next reviewer questiondiff_id: stringwait_seconds?: integer
reply_to_branch changes: Review mode only: post an answer to a reviewer's questiondiff_id: stringcomment_id: stringcontent: stringpartial?: boolean
list_open_branches: Review mode only: list the review's open questions without claiming themdiff_id: string

Popularity

73 popularity score, on our list (the bar is 36)

★ 3.4k ↓ 5.8k/wk

GitHub stars	3,442	42.4 points
npm downloads, last week	5,834	30.1 points

Measured 2026-11-07. How the score works.

Where it is published

Code	ataraxy-labs/sem ★ 3.4k
npm	@ataraxy-labs/sem 0.29.1, 2026-11-02

What it can reach

Runs	On your machine
Reaches	Files on your machine, Your code, Runs shell commands, The internet
Changes things	Yes: it can write, send, create or delete
Sign-in	None
Licence	MIT OR Apache-2.0 (npm)
Usage data	Only if you turn it on (`sem config telemetry on\|local\|off, or SEM_TELEMETRY`) Command name, sem version, OS and a timestamp, with an install id that changes daily; counted locally by default and uploaded to sem-cloud.fly.dev only in on mode
Last code change	2026-11-06

Runs locally and reads the source files and Git history of one repository. It writes its entity cache and query index to the OS cache directory. sem_check runs the project's build, type-check, lint and test commands, or any command passed in `run`, with your permissions. Default tools need no account; in `sem mcp --review` mode the review tools contact Ataraxy Labs' cloud and post replies to a review. The HTTP preview listens on loopback only, requires a bearer token and rejects browser Origin requests; its docs say it is no sandbox and any token holder can read the checkout. Separately, the CLI command `sem config setup` edits ~/.claude/settings.json on macOS and Linux to add hooks that run on each prompt and around Edit, Write and MultiEdit; `sem config unsetup` removes them.

Over time

GitHub stars 3.4k +31 (+1 %)

3.4k3.4k

14 Oct 20267 Nov 2026

npm downloads a week 5.8k +5.2k (+779 %)

10.0k454

20 Apr 20267 Nov 2026

Before the site measured it, read from npm's daily download counts.

Popularity score 73 +1 (+1 %)

7368

14 Oct 20267 Nov 2026

What is rising across the directory

Sources

Page checked 2026-10-26.

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MarkdownREADME.md

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Connect your client

Add in one click

Or add it by command or config

Add in one click

Or add it by command or config

Settings 6

What it does

What it needs

Limits

Who it suits

Tools 12

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