Web-Algebra: Composable RDF operations system for Linked

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Martynas JusevičiusMaker

What Linked Data operations would you like to see supported in Web-Algebra?

About Web-Algebra

Web-Algebra exposes RDF Linked Data and SPARQL operations as MCP tools. Claude can read and write Linked Data over HTTP (GET, PUT, POST, PATCH), run SPARQL SELECT, CONSTRUCT and DESCRIBE queries, merge graphs and build URIs. It also covers LinkedDataHub: creating containers and items, adding content blocks and views, and extracting an ontology from a dataset.

Operations compose. Besides calling tools one at a time, an agent can write a whole workflow as a JSON plan of nested operations (including ForEach over query results) and the execution engine runs it in one step. Web-Algebra can also translate natural-language instructions into such plans on its own, which requires an OpenAI key.

Install: uvx --from web-algebra web-algebra-mcp. The generic Linked Data and SPARQL tools need no configuration. LinkedDataHub operations need CERT_PEM_PATH and CERT_PASSWORD (the owner certificate). Apache-2.0.

How it was built with Claude

Mostly with Claude Code. About 100 of the repo's 232 commits are co-authored with Claude.

What worked best was writing the spec first. formal-semantics.md defines the evaluation model (borrowed from XPath/XSLT: flat sequences, a focus of Current/Position/Last, typed errors) and the catalogue of operations. Claude Code then implements and tests against that spec instead of guessing. An AGENTS.md file, which CLAUDE.md imports, holds the repo conventions, so every session starts from the same rules.

The examples directory doubles as a test suite. Each example is a real plan over live Linked Data (Northwind, UNESCO thesaurus, city profiles) with its expected result and checks. When Claude changes an operation, the examples tell it whether the plans still run.

Claude is also the main user. With the MCP server connected, Claude Desktop and Claude Code call the operations directly or write whole JSON plans, so I could test the tool descriptions by watching how Claude used them and rewording the ones it misread.