prism

README

Prism

Graph-ranked code context for AI coding agents.

Prism turns a task plus a few precise anchors into the code, callers, callees, tests, docs, and coverage gaps an agent needs to make a change safely.

Prism is not a better grep. Use rg/grep to find the first anchor. Use Prism to answer the follow-up questions that usually cost several file reads:

• What calls this?
• What does this call?
• Which tests define the contract?
• What else is in the blast radius?
• Which nearby exported functions have no direct test coverage?

The recommended agent mode is both (MCP tools as primary surface, CLI fallback for subagents that don't inherit the MCP session):

prism init . --mode both

Agents with an active MCP session call prism_query, prism_read, and prism_lookup directly. Subagents and CI scripts fall back to the CLI:

prism query "fix direct coverage gaps" --terms buildCoverageGaps --include graph,tests,coverage_gaps --format text
prism read internal/mcp/tools.go --format text
prism lookup github.com/provasign/prism/internal/mcp.buildCoverageGaps --format text

--format text avoids the large JSON metadata wrappers that made early MCP benchmarks look expensive. Agents see plain source-like context with short headers, and can ask for lean or json only when automation needs it.

Grove is embedded in the Prism binary. There is no separate daemon, token, or grove_url setup in current releases.

---

Why Prism

Shell search gives pointers. Agents still have to chase those pointers by reading files, guessing test names, and manually reconstructing call paths.

Prism precomputes the project graph and lets the agent ask for relationships:

rg buildCoverageGaps internal/
  -> prism query "write tests for buildCoverageGaps" \
       --terms buildCoverageGaps \
       --include graph,tests,coverage_gaps \
       --format text

On this repository, five real maintenance scenarios were run both ways on 2026-06-07. Shell-only baselines used rg plus targeted sed reads; Prism used one CLI text command per scenario.

Scenario	Shell bytes	Prism CLI bytes	Context reduction
Init agent_mode / CLI steering impact	19,970	12,818	35.8%
coverage_gaps precision	21,226	17,145	19.2%
CLI text/lean/json output formatting	15,820	14,198	10.3%
Session cache / savings ledger	33,134	19,922	39.9%
Release/version/install wiring	21,246	12,157	42.8%

The average reduction was 29.6% with one Prism command instead of 5-6 shell commands. The bigger correctness win is that Prism surfaces tests and coverage gaps proactively; shell-only workflows often discover those after CI fails.

A controlled A/B re-run (2026-06-12, post Grove-v0.6.2 fixes) on the payflow ground-truth project: zero coverage false positives at the tool level, total agent-token parity with the shell baseline (the 2026-06-07 run had +27–147% overhead), 47 vs 84 tool calls, and the baseline agent missing 3 of 12 designed coverage gaps that coverage_gaps reports mechanically. Repeat reads cost 29 tokens (95% saved); a rename under the agent's feet is reported as one breaking renamed entry for ~130 tokens. Full report: docs/AB-Test-Payflow-2026-06-12.md.

More detail, including repeat-read savings: provasign.dev/prism.

---

How It Works

Task + anchor terms
      |
      v
Embedded Grove index
  - symbols
  - call edges
  - dependency edges
  - test edges
      |
      v
Prism ranking
  - graph distance
  - semantic similarity
  - recency
  - test relevance
  - edit frequency / learned weights
      |
      v
Budgeted text context
  - target symbols
  - callers/callees
  - tests
  - docs
  - coverage_gaps

Prism supports two distinct saving mechanisms:

1. Context gathering reduction: one graph-aware query replaces multiple shell searches and file reads. This is what CLI text-mode benchmarks measure.
2. Session deduplication: in persistent MCP transports, repeated reads of unchanged files can become a short SHA pointer. This is where the ~99% repeated-read savings come from.

Direct CLI invocations are process-per-command, so they should be evaluated on context gathering and output wrapper size, not same-session re-read dedupe.

---

Installation

# Homebrew (macOS / Linux) — one tap for the family (prism, fuse, shale)
brew install provasign/shale/prism

# macOS / Linux script
curl -fsSL https://raw.githubusercontent.com/provasign/prism/main/install.sh | bash

# Windows PowerShell
irm https://raw.githubusercontent.com/provasign/prism/main/install.ps1 | iex

# Pin a version
VERSION=v0.7.0 curl -fsSL https://raw.githubusercontent.com/provasign/prism/main/install.sh | bash

The installer writes prism to ~/bin by default. Set INSTALL_DIR=/usr/local/bin or another directory to override.

Build from source:

make build
make test
make install

---

Quick Start: Agent CLI Text Mode

Run this once at the project root:

prism init . --mode both
prism index .

This writes:

• prism.yaml with agent_mode: "both"
• .mcp.json wiring the MCP server for MCP-capable clients
• steering files such as AGENTS.md, CLAUDE.md, .cursorrules, .windsurfrules, .github/copilot-instructions.md, and others
• compatible tool config files where detected

The generated agent instructions tell agents to use commands like:

prism query "trace the payment refund flow" --terms RefundPayment --include graph,tests --format text
prism query "find direct coverage gaps" --terms UpdatePayment,RequireScope --include graph,coverage_gaps --format text
prism read internal/payment/service.go --format text
prism lookup github.com/example/payflow/internal/payment.(*Service).RefundPayment --format text

Recommended agent workflow:

1. Locate the first anchor with rg, grep, or find.
2. Run prism query with the same anchor terms.
3. Use prism read for whole files only when needed.
4. Use prism lookup for one known function or method.
5. Treat coverage_gaps as a terminal structured output, not the start of manual cross-referencing.

---

Other Modes

prism init supports three modes:

prism init . --mode both  # recommended: MCP primary + CLI fallback for subagents
prism init . --mode mcp   # MCP tools only: prism_query, prism_read, ...
prism init . --mode cli   # CLI only: for environments without MCP support

MCP

MCP advertises six tools: prism_query, prism_read, prism_search, prism_lookup, prism_index, and prism_drift. The auxiliary tools (prism_savings, prism_feedback, prism_compact, prism_evidence) stay available through the CLI and HTTP server without spending schema tokens in every MCP session. Use MCP when the client has first-class MCP support and you want persistent session deduplication.

HTTP Server

prism serve is optional. Use it for custom automation that wants HTTP instead of CLI or MCP:

prism serve --port 8888 /path/to/project

It binds to 127.0.0.1.

---

CLI Reference

prism init [--global] [--mode cli|mcp|both] [dir]
prism index [dir]
prism status [dir]

prism query <task> [dir] \
  --terms a,b,c \
  --include graph,tests,docs,coverage_gaps \
  --depth 2 \
  --format text

prism read <file> [dir] --format text
prism lookup <name> [dir] --format text
prism search <keyword> [dir] --format text
prism savings [dir]
prism compact [dir]
prism feedback --tool <name> --rating <0-5> [dir]
prism mcp [dir]
prism serve [--port 8888] [dir]
prism version

Output formats:

Format	Use
text	Default and recommended for agents
lean	Compact JSON without most metadata
json	Full metadata for tooling/debugging

---

Configuration

prism.yaml is intentionally small:

version: 1
profile: "default"
agent_mode: "cli"

Optional keys:

model: "claude-sonnet-4-6"
grove_binary: "grove"
embeddings_backend: "tfidf"

Environment overrides include PRISM_MODEL, PRISM_PROFILE, PRISM_GROVE_BINARY, and PRISM_EMBEDDINGS_BACKEND.

---

Language Support

Prism delegates parsing and graph construction to embedded Grove.

Language	Extensions
Go	.go
TypeScript / TSX	.ts, .tsx
JavaScript / JSX	.js, .jsx, .mjs, .cjs
Python	.py
Java	.java
Rust	.rs
C / C++	.c, .h, .cc, .cpp, .hpp, ...
C#	.cs
PHP	.php, .phtml, ...

Markdown, YAML, JSON, shell scripts, Dockerfiles, Makefiles, SQL, GraphQL, and other non-code files are indexed as document symbols and can be requested with --include docs.

---

Benchmarks

The headline numbers (context reduction per scenario, repeat-read savings by project size, and the SHA-pointer dedup mechanism) are summarized with methodology at provasign.dev/prism. The full benchmark reports were trimmed from this repo to keep it lean; they remain available in git history (git log --diff-filter=D -- docs/ to locate them).

Current practical summary:

• CLI --format text is the recommended default for shell-capable agents.
• Prism is strongest on graph/blast-radius/test/coverage-gap questions.
• Shell tools remain best for locating exact strings or filenames.
• MCP persistent transports add repeated-read deduplication that direct CLI invocations do not fully exercise.

---

Troubleshooting

prism query returns nothing: run prism index . from the project root.

Agent uses wrong steering: run prism init . --mode both (or your chosen mode) and verify prism.yaml has the correct agent_mode.

Wrong Prism binary: run command -v prism and prism version. Reinstall if the version is old.

macOS quarantine:

xattr -d com.apple.quarantine "$(which prism)"
codesign -f -s - "$(which prism)"

MCP client does not connect: restart the coding tool after prism init, and approve project MCP configuration if the tool prompts.